Image capturing device

ABSTRACT

An image capturing device includes an image forming device including a sensor defining an optical reception axis, at least one reading distance, and a region framed by the sensor on a substrate at said at least one reading distance. An illumination device includes an array of adjacent light sources defining an optical illumination axis. The light sources are individually drivable, and each light source is adapted to illuminate an area of a size much smaller than the size of said region framed by the sensor. The illumination axis does not coincide with the reception axis. A driver of the light sources is adapted to drive the light sources so as to switch off at least the light sources that illuminate outside of the boundary of the region framed by the sensor on the substrate at said at least one reading distance.

The present invention concerns an image capturing device and inparticular such a device of a reading system or reader of opticalinformation of the “imager” type.

Imager type readers of optical information are well known. Such readerscomprise an image capturing device capable of capturing or acquiring theimage of optical information present on a substrate of whatever kind,including a display on which the optical information is displayed inturn by whatever electrical or electronic device.

In the present description and in the attached claims, the expression“optical information” is used in its widest sense to include bothone-dimensional, stacked and two-dimensional optical codes, in whichinformation is encoded in the shapes, sizes, colours and/or reciprocalpositions of elements of at least two distinct colours, and alphanumericcharacters, signatures, logos, stamps, trademarks, labels, hand-writtentext and in general images, as well as combinations thereof, inparticular present on pre-printed forms, and images containing featuressuitable for identifying and/or selecting an object based on its shapeand/or volume.

In the present description and in the attached claims, the term “light”is used in its widest sense, indicating electromagnetic radiation of awavelength or of a range of wavelengths not only in the visiblespectrum, but also in the ultraviolet and infrared spectra. Terms suchas “colour”, “optical”, “image” and “view” are also used in the samewidest sense. In particular, the encoded information can be marked on asubstrate in invisible ink, but sensitive to ultraviolet or infraredrays.

Imager type readers of optical information typically comprise, inaddition to the image capturing device, devices having one or moredifferent other functions, or are in communication therewith.

Among such further devices are mentioned herein: a device for processingthe captured image, capable of extracting the information content fromsuch an image or from a portion thereof; a memory device; a device orinterface for communicating the acquired image and/or the extractedinformation content outside the reader; a device or interface forinputting configuration data for the reader, coming from an externalsource; a device for displaying to the user alphanumeric and/orgraphical information relating for example to the operative state of thereader, the content of the information read, etc.; a device for manuallyinputting control signals and data; an internal device for supplyingpower, or for taking a power supply signal from the outside.

Moreover, among the further devices that can be included in orassociated with an imager type optical information reader are mentionedherein: an aiming device that aids the operator in positioning thereader with respect to the optical information by displaying on thesubstrate a visual indication of the region framed by the imagecapturing device, for example its centre and/or at least part of itsedges and/or corners; an aid device for correctly focussing the imagecapturing device (rangefinder), which displays on the substrate aluminous figure having variable shape, size and/or position between afocussed condition and an out-of-focus condition, and possiblyindicative of the direction in which to mutually move the imagecapturing device and the substrate to reach the focussed condition; anoutcome indication device, which displays on the substrate a luminousfigure indicative of the positive or negative outcome, and possibly ofthe reasons for a negative outcome, of an attempt at capturing an imageand/or decoding the optical information, through variations in shape,size, colour and/or position of the luminous figure; a device fordetecting the presence of a substrate and/or for measuring or estimatingthe reading distance, namely the distance between a reference in thereader, in particular a sensor of the image capturing device, and thesubstrate. The functions of targeting and indicating focus can also bemade together through the projection of a suitable luminous figure, forexample a pair of inclined bars or a pair of crosses, respectively, thatcross each other at their centres or superimpress to each other,respectively, at the centre of the region framed by the image capturingdevice only at the focused distance.

The measurement or estimate of the distance is typically used by thereader to activate the decoding algorithm only when the opticalinformation is located at a distance comprised between the minimum andmaximum working distance, and/or to control a zoom device and/or adevice for automatically changing the focussing distance of the imagecapturing device (autofocus). Moreover, the measurement or estimate ofthe distance can be used in the case in which digital restoration of theimage is necessary, since the degrading function, or the PSF (pointspread function) of the optics of the image forming device, depends uponthe reading distance. Furthermore, the measurement or estimate of thedistance is necessary to calculate the volume of an object.

Devices for aiming and/or indicating focus are for example described inU.S. Pat. No. 5,949,057, U.S. Pat. No. 6,811,085, U.S. Pat. No.7,392,951 B2, in U.S. Pat. No. 5,331,176, in U.S. Pat. No. 5,378,883 andin EP 1 466 292 B1.

Outcome indication devices are described, for example, in theaforementioned document U.S. Pat. No. 5,331,176 and in EP 1 128 315 A1.

It is worth emphasising that each of the functions of aiming, indicationof the focus condition, outcome indication, detection of presence andmeasurement or estimate of the reading distance can be implemented indifferent ways that are per se well known and do not exploit theprojection of light on the substrate. Purely as an example are quotedherein, for the aiming and/or the focus condition, viewfinders anddisplays of what is framed by the sensor; for the indication of outcome,sound indications and visual indications projected not on the substrate,rather towards the operator; for the detection of presence, measurementor estimate of the distance and/or evaluation of the focus condition,photocell systems, radar or ultrasound devices, etc.

An image capturing device of the imager type comprises an image formingdevice or section, comprising a sensor in the form of an orderedarrangement or array—linear or preferably of the matrix type—ofphotosensitive elements, capable of generating an electric signal froman optical signal, and typically also a receiver optics of the image,capable of forming an image of the substrate containing the opticalinformation, or of a region thereof, on the sensor.

The image capturing device is characterised by an optical receptionaxis, which is defined by the centres of the elements of the receiveroptics, or by the centres of curvature of the optical surfaces in thecase of a single lens, and which defines its main working direction. Theimage capturing device is also characterised by a working space region,generally shaped like a frustum of pyramid, extending in front of thesensor. The working space region, in other words the region of space inwhich optical information is correctly framed by the sensor and theimage of which is sufficiently focussed on the sensor, is usuallycharacterised through a field of view, which expresses the angular widthof the working region about the reception axis, and a depth of field,which expresses its size along the direction of the reception axis. Thedepth of field therefore expresses the range between the minimum andmaximum useful distances, along the reception axis, between the readerand the region on the substrate framed by the sensor. The field of viewcan also be expressed in terms of “vertical” and “horizontal” field ofview, in other words in terms of two angular sizes in planes passingthrough the reception axis and perpendicular to each other, to take dueaccount of the shape factor of the sensor, or even, in the case ofreception system without any symmetry, four angular sizes in half-planes90° apart.

The working space region—and therefore the field of view and the depthof field—can be fixed or made dynamically variable in size and/or inproportions through well known zoom and/or autofocus systems, such aselectromechanical, piezoelectric or electro-optical actuators for movingone or more lenses or diaphragms, mirrors or other components of thereceiver optics or for moving the sensor, and/or for changing thecurvature of one or more lenses of the receiver optics, such as liquidlenses or deformable lenses.

EP 1 764 835 A1 describes an optical sensor wherein each photosensitiveelement or group of photosensitive elements has an associated lens orother optical element, such as diaphragms, prismatic surfaces, lightguides or gradient index lenses. Such a document is totally silent aboutthe illumination of the region framed by the sensor.

Although image, capturing devices operating with ambient light only arewell known, the image capturing device of the imager type typicallyfurther comprises an illumination device or section suitable forprojecting one or more beams of light, possibly variable in intensityand/or spectral composition, towards the substrate carrying the opticalinformation. The beam of light emitted by the illumination device, orthe whole of the beams of light, defines an optical illumination axis,which is the average direction of such a single or composite light beam,being an axis of symmetry thereof in at least one plane and typically intwo perpendicular planes in the case of a two-dimensional array.

For correct operation of the image capturing device, the illuminationdevice must be able to illuminate the entire working space region of theimage forming device.

An image capturing device wherein, as illustrated in FIG. 1—and which isanalogous to that of FIG. 4 of U.S. Pat. No. 5,378,883 referred toabove—, the illumination device 90 is not coaxial with the image formingdevice 91, rather is arranged alongside the image forming device 91 andconfigured so that the illumination axis 92 of the illumination beam 93and the reception axis 94 converge, is subject to an intrinsic parallaxerror and to an intrinsic perspective distortion error in thetwo-dimensional case. Such errors make the intersection between thesubstrate S and the illumination beam 93 and the intersection betweenthe substrate S and the working space region 95 of the image formingdevice 91 substantially concentric at most in a very small range ofreading distances (about the distance where the substrate S is partlyindicated in FIG. 1). Consequently, in order to that the illuminationdevice 90 is able to illuminate the entire working space region 95 ofthe image forming device 91, at most of the reading distances theillumination is overabundant (cfr. the distances where the substrate S₁or the substrate S₂ is partly indicated in FIG. 1), in other words theillumination extends outside of the region framed by the sensor on thesubstrate, with consequent waste of energy.

In some devices for capturing images of the prior art, the parallaxerror is solved by making the illumination device coaxial to the imageforming device.

U.S. Pat. No. 5,319,182 describes an image capturing device, not of theimager type but rather of the scanning type, wherein the illuminationdevice and the sensor are overall coaxial, in that they consist of amatrix in which emitters with programmable activation alternate with thephotosensitive elements of the sensor. This device is potentially verycompact and flexible, but it is also subject to remarkable problems ofoptical insulation between the emitters and the photosensitive elements:even by providing for an insulator between them as suggested in thedocument, the light emitted by the emitters and reflected, even to aminimal extent, onto the photosensitive elements by any surface, such asan opaque dividing wall or the rear surface of a projection optics withanti-reflection treatment, is of much higher intensity than thatreceived from the substrate carrying the optical information. Moreover,laying out on a single substrate photosensitive elements andphoto-emitting elements leads to compromises in terms of efficiencysince the required characteristics of the material in order to haveefficient photo-emitting elements are the opposite to those required toobtain efficient photosensitive elements.

In U.S. Pat. No. 5,430,286 the coaxiality between the light emitted bythe illumination device and the image forming device is obtained througha beam splitter. As a result there are a very large space occupied inthe reader and a very low efficiency, due to the loss of 50% of powerboth along the illumination path and along the reception path.

Such a system, also suffering from problems of occupied space, isdescribed in the aforementioned U.S. Pat. No. 5,331,176, which uses asemi-transparent mirror instead of the beam splitter. Such a documentalso teaches to adjust the size of the section of the illumination beam,but through mechanical moving devices that contribute to the occupiedspace and to the consumption of the reader. Moreover, such a solutiondoes not avoid the drawback of wasting energy for illumination, since aportion of the illumination beam is merely obscured.

US 2007/0158427 A1, which represents the closest prior art, in FIG. 5Bdescribes an illumination system comprising a pair of illuminationarrays each arranged on opposite sides of the sensor and associated withthe greater working distances, and a pair of illumination arrays, alsoeach arranged at said opposite sides of the sensor and associated withthe smaller distances. Since the section of the light beam overallemitted by the pair of arrays associated with the greater workingdistances is oriented and sized to uniformly illuminate the entireregion framed by the sensor at least at the maximum distance, it followsthat at such a distance and at the shorter reading distances theillumination by such arrays is overabundant, in other words it extendsoutside of the region framed by the sensor. This kind of drawback occurswith regard to the pair of arrays associated with the smaller workingdistances. The device of such a document is therefore scarcelyefficient, in particular scarcely suitable for battery-powered portablereaders, where energy saving is an important requirement. The documentalso teaches to switch on only one array of each pair to avoid problemsof reflection from the substrate, therefore falling into the case of asystem subject to parallax and perspective distortion errors, or toswitch on both of the pairs of arrays when the reading distance isunknown. The document further describes a further pair of illuminators,each arranged at the other two sides of the sensor, to illuminate a thinline for reading one-dimensional codes, and four illuminators for aiminga region of interest, arranged at the vertexes of the sensor.

The technical problem at the basis of the invention is to provide anefficient image capturing device, and more specifically such a device ofan imager type reader of optical information, which in particular isfree from parallax error, still without providing overabundantillumination, extending outside of the region framed by the sensor, andwhich avoids any possibility of optical interference between lightsources and photosensitive elements.

In a first aspect thereof, the invention concerns an image capturingdevice of the imager type, comprising:

-   -   an image forming device including a sensor including a        one-dimensional or two-dimensional array of photosensitive        elements and defining an optical reception axis, at least one        reading distance, and a region framed by the sensor on a        substrate at said at least one reading distance,    -   an illumination device including an array or array of adjacent        light sources, defining an optical illumination axis,        characterised:    -   in that the light sources are individually drivable and each        light source is adapted to illuminate an area of a size much        smaller than the size of said region framed by the sensor,    -   in that the illumination axis does not coincide with the        reception axis,    -   by comprising a driver of the light sources adapted to drive the        light sources so as to switch off at least the light sources        that illuminate outside of the boundary of the region framed by        the sensor on the substrate at said at least one reading        distance.

In the present description and in the attached claims, the term “opticalreception axis” is meant to indicate the direction defined by thecentres of the elements of the receiver optics, or by the centres ofcurvature of the optical surfaces in the case of a single lens.

In the present description and in the attached claims, the term “opticalillumination axis” is meant to indicate the average direction of themaximum illumination beam that would be emitted by the illuminationdevice if all of the light sources of the array were switched on—apartfrom a possible different angular blur of the sources at oppositeextremes of the array.

It should be noted that in the present description and in the claims theterm “axis” is used for the sake of simplicity, although in practice inboth cases it is a half-axis.

In the present description and in the attached claims, under “adjacent”it is meant to indicate that between the light sources there are nocomponents having different functions from the light emitting functionand/or from a function slaved to this, like for example addressing,driving, heat dissipation, optical insulation of the light sources; sucha term must not therefore be construed in a limiting sense to indicatethat the light sources are in contact with each other.

In the present description and in the attached claims, under “boundary”of the region framed by the sensor on the substrate it is meant toindicate a line having a thickness equal at most to the regionilluminated by an individual light source of the array. In other words,the terminology takes into account the fact that the light sources arein any case finite in number, and that every light source illuminates aregion having a finite size, thus dictating a resolution limit of theillumination system with respect to the geometric boundary of the regionframed by the sensor.

Each individually drivable light source preferably comprises anindividual illuminating element, but it could comprise more than one.

Preferably, said at least one reading distance comprises a plurality ofreading distances within a depth of field, in other words a plurality ofreading distances between the minimum reading distance and the maximumreading distance inclusive.

The reading distances at which the driver is adapted to drive the lightsources so as to switch off at least the light sources that illuminateoutside of the boundary of the region framed by the sensor on thesubstrate can be discrete from one another, or variable with continuitywithin the depth of field.

Typically, in order to increase the depth of field and/or to betterdefine the direction and/or the shape in space of the region framed bythe sensor, the image forming device further comprises at least onereceiver optics, with fixed or variable focal length. Such a receiveroptics can in particular comprise a single lens or optical group sharedby the photosensitive elements of the sensor and/or an array of lenses,prismatic surfaces and/or diaphragms each associated with aphotosensitive element or sub-group of elements, for example asdescribed in the aforementioned EP 1 764 835 A1.

Typically, the image forming device comprises a zoom and/or autofocussystem, in which case the region framed by the sensor is variable in away not directly proportional to the reading distance within the depthof field.

The reception axis can coincide with the normal to the plane of thesensor or be inclined with respect to it by an angle.

Preferably, in order to increase the focal depth on the image sideand/or to incline the illumination axis with respect to the normal tothe array of light sources, the latter is associated with at least oneprojection lens. More specifically, each light source can be providedwith its own projection lens, and/or at least one single projection lenscan be provided, shared by the light sources of the array.

Each projection lens can be replaced by or associated with other opticalelements, such as diaphragms, prismatic surfaces, light guides and/orgradient index lenses, in an analogous way to what is described in theaforementioned EP 1 764 835 A1.

The illumination axis can coincide with the normal to the plane of thearray or be inclined with respect to it by an angle.

In some embodiments, the illumination axis is parallel to and spacedfrom the reception axis.

In other embodiments, the illumination axis is inclined and not coplanarwith respect to the reception axis. In the case in which the two axesare inclined, they can intersect, generally in front of the sensor, orelse they can be oblique.

In some embodiments, the array and the sensor are coplanar, so that theycan advantageously be made on a same support, on a same integratedcircuit board, or be made on a same integrated circuit substrate.

In other embodiments, the array and the sensor are arranged on planesinclined to each another, so that advantageously the angle ofinclination between the illumination axis and the reception axis isdetermined or is contributed to being determined.

Preferably, the light sources of the array are adapted to overallilluminate, if all of them were switched on, a larger area than themaximum region framed by the sensor within the depth of field.

More specifically, the number of light sources is selected so that thearea overall illuminated on the substrate by the illumination deviceundergoes a sufficiently small percentage change when a single lightsource is switched on/off.

Preferably, the percentage change is less than or equal to 15%, morepreferably less than or equal to 10%, even more preferably less than orequal to 5%.

Preferably, the driver is adapted so as not to switch on all of thelight sources of the array at any reading distance.

More preferably, the driver is adapted to switch off at least one lightsource at an edge of the array at each reading distance. In other words,the driver is adapted so as not to switch on both of the light sourcesarranged at opposite extremes of the array at any reading distance.

Preferably, the driver is adapted to switch off all of the light sourcesthat illuminate outside of the boundary of the region framed by thesensor at the reading distance, and to switch on all of the sources thatilluminate within the boundary of the region framed by the sensor in anoperating mode.

Preferably, the driver is adapted to switch on only the light sourcesthat illuminate at least one region of interest within the region framedby the sensor in an operating mode.

The driver can respond to a measurer of, or device for estimating, thereading distance.

The measurer of the reading distance can be a distinct device from thereader and in communication with it, for example a system of photocells,a device based on the measurement of the phase or of the time of flightof a laser or LED beam, visible or IR, or of the radar or ultrasoundtype, etc.

Preferably, however, the driver is adapted to switch on light sources ofthe array selected to project a luminous figure for evaluating thereading distance in an operating mode. The reading distance is measuredor estimated based on the shape and/or position of the image formed onthe sensor by the light emitted by said at least some of the lightsources of the array.

The driver can be adapted to switch on light sources of the arrayselected to overall illuminate a luminous figure for aiming the regionframed by the sensor and/or at least one region of interest thereof inan operating mode.

The driver can be adapted to switch on light sources of the arrayselected to overall illuminate a luminous figure for indicating anoutcome of an attempt at capturing an image within the region framed bythe sensor in an operating mode.

The light sources of the array are preferably individually drivable alsoin the intensity of emission.

Preferably, the array of light sources is suitable for emitting light ofmore than one wavelength. In particular, the array can comprise a firstsub-plurality of light sources suitable for emitting at a firstwavelength and at least one second sub-plurality of light sourcessuitable for emitting at a different wavelength from the firstwavelength. Alternatively, each light source can be suitable forselectively emitting light of different wavelengths.

With such a provision it is for example possible to adjust the colour ofthe illumination based on the colour of an optical code and itsbackground. Moreover, it is possible to easily provide a diversifiedindication of outcome of the capture or reading attempt, for example byprojecting a green luminous figure for a positive outcome and a redluminous figure for a negative outcome. Furthermore, it is possible todiversify the luminous figures for aiming plural regions of interest,also for the sake of their selection by the user.

The array of light sources can be one-dimensional or two-dimensional.

The array of light sources can be flat or curved. By arranging the lightsources on a curved surface it is possible to make the lengths of theoptical paths between each light source and the substrate the same orsubstantially the same, therefore compensating for the differentattenuation that the light emitted by the light sources would undergo inthe case of a flat array, and therefore obtaining illumination ofuniform intensity at the reading distance. A curved arrangement can alsobe used to determine or contribute to determining the divergence of theillumination beams of the various light sources.

Preferably, the number of light sources of the array is greater than orequal to 32 in the one-dimensional case, or 32×32 in the two-dimensionalcase, respectively.

More preferably, the number of light sources of the two-dimensionalarray is selected from the group consisting of 32×32, 64×64, 44×32 and86×64, and in the one-dimensional case it is selected from the groupconsisting of 32 and 64.

In an embodiment the driver is adapted to switch off at least all of thesources that illuminate outside of the boundary of a first half of theregion framed by the sensor at the reading distance, the image capturingdevice further comprising a second array of individually drivable,adjacent light sources, defining a second illumination axis, the secondillumination axis not coinciding with the reception axis, and the driverof the light sources being adapted to drive the light sources of thesecond array so as to switch off at least the light sources thatilluminate outside of the boundary of a second half of the region framedby the sensor complement to the first half.

In an embodiment, the image capturing device further comprises a secondarray of individually drivable, adjacent light sources, defining asecond illumination axis, the second illumination axis not coincidingwith the reception axis, and the driver of the light sources beingadapted to drive the light sources of the second array so as to switchoff at least the light sources that illuminate outside of the boundaryof the region framed by the sensor.

In an embodiment the driver is adapted to run-time determine which lightsources of the array to switch on or off, respectively, as a function atleast of the reading distance.

In embodiments, the run-time determining is carried out through ananalytical method, in other words making use of analytical formulae thatdepend only upon known (design) geometric parameters of the reader, andin particular of its image forming device, of its illumination deviceand/or of their relative spatial arrangements, including the relativespatial arrangement of their components or subassemblies.

Preferably, the analytical method comprises the steps of:

-   -   in a first reference system associated with the reception        device, calculating the coordinates of peculiar points of the        region framed on the substrate by the sensor;    -   carrying out a transformation of coordinates into a second        reference system associated with the illumination device; and    -   in the second reference system, calculating the light sources of        the array that illuminate corresponding peculiar points.

Preferably, in the aforementioned steps one or more of the formulae from(1) to (31) described below are implemented.

In embodiments, the run-time determining is carried out at least in partthrough an empirical or adaptive method, comprising, in a recursivemanner, driving so as to switch on a subset of light sources, evaluatingthe position and/or extent of the illuminated area on the substrate withrespect to the region framed by the sensor, and adapting the subset oflight sources based on such an evaluation.

The initial subset of light sources can be determined in advance in ananalytical manner, the empirical or adaptive method thus being used forexample to correct imprecisions of the array of light sources of eachimage capturing device of a production batch.

In embodiments, said recursive adaptation of the subset of light sourcesto be switched on is carried out along a plurality of radially spaceddirections.

In embodiments, the subset of light sources to be switched on isdetermined by an interpolation of the positions of the extreme lightsources to be switched on along said plurality of directions.

In an alternative embodiment, the driver is adapted to determine whichlight sources to switch on or off, respectively, as a function of thereading distance by reading them from a look-up table.

The driver can be adapted to build one-off (una tantum) said look-uptable, in particular with analytical or empirical/adaptive method,similarly to the run-time determining.

Alternatively, the driver can be adapted to receive as an input saidlook-up table, one-off built by a separate processing device, withanalytical or empirical/adaptive method, similarly to the run-timedetermining.

Should the determining of the light sources to be switched on or off,respectively, as a function of the reading distance one-off occur in aseparate processing device, it is preferably implemented by a computerprogram that parametrically manages one or more quantities of the imagecapturing device. In this way, advantageously the same computer programcan be used for example for a range of reader models.

Such a computer program represents a further aspect of the invention.

The light sources of the array are preferably of the solid state type orare organic, and more preferably they are selected from the groupcomprising LEDs, OLEDs, microLEDs and microlasers.

In another aspect thereof, the invention concerns an imager type readerof optical information comprising an image capturing device as describedabove.

In another aspect thereof, the invention concerns a computer readablememory means comprising the aforementioned program.

In another aspect thereof, the invention concerns an optical readercomprising an array of individually drivable, adjacent light sources,and a driver adapted to drive the light sources of the array in anillumination mode, an aiming mode, and a reading outcome indicationmode.

Preferably, said driver is also adapted to drive the light sources in anoptical distance measurement system or measurer mode.

Further characteristics and advantages of the invention will be betterhighlighted by the description of some embodiments thereof, made withreference to the attached drawings, in which:

FIG. 1, already described in detail, illustrates an image capturingdevice of the prior art, wherein an illumination device is not coaxialto an image forming device,

FIG. 2 schematically illustrates an imager type reader of opticalinformation according to the invention,

FIG. 3 schematically illustrates an image capturing device according tothe invention,

FIG. 4 illustrates, in greatly enlarged scale, a portion of an array ofmicroLEDs with pre-collimation lens on each light source,

FIG. 5 illustrates the illumination of a flat array of light sources ofan illumination device not coaxial with the image forming device,

FIG. 6 illustrates the illumination of a curved array of light sourcesof an illumination device not coaxial with the image forming device,

FIGS. 7 to 9 are block diagrams that illustrate some embodiments of thedriving of the light sources of the illumination device,

FIGS. 10 to 17 are representations of the geometry of the imagecapturing device or of parts thereof,

FIG. 18 is a block diagram that illustrates another embodiment of thedriving of the light sources of the illumination device,

FIG. 19 is a graphical representation of the embodiment of the drivingof the light sources of the illumination device of FIG. 18,

FIG. 20 is a graphical representation of an embodiment of the driving ofthe light sources of the illumination device,

FIGS. 21 a, 21 b and 21 c represent as a whole a block diagram thatillustrates in detail the embodiment of the driving of the light sourcesof the illumination device represented in FIG. 20,

FIGS. 22 to 27 are schematic representation of various embodiments ofthe image capturing device,

FIG. 28 is a representation of the geometry of an embodiment of theillumination device of the image capturing device,

FIG. 29 illustrates the light sources of the image capturing device ofan embodiment to be switched on to illuminate the entire region framedby the sensor at various working distances,

FIGS. 30 to 37 schematically illustrate further functions of theillumination device of the image capturing device,

FIGS. 38 and 39 schematically illustrate other embodiments of the imagecapturing device.

FIG. 2 is the block diagram of a reading system or in short reader 1 ofan imager type optical information according to the invention.

The reader 1 comprises an image capturing device 2 capable of capturingor acquiring the image of optical information C, exemplified in FIG. 2by a two-dimensional optical code, present on a substrate S.

The image capturing device 2, better described hereinafter, comprises animage forming device or section 3, comprising a sensor 4 in the form ofan array—linear or preferably of the matrix type as shown—ofphotosensitive elements, capable of generating an electrical signal froman optical signal, in other words from the light R emitted by thesubstrate S, which is modulated by the graphical elements present, inparticular by the code or other optical information C.

The image forming device 3 further typically, even if not necessarily,comprises an image reception optics 5, capable of forming on the sensor4 an image sufficiently focused of the substrate S containing theoptical information C, or of a region thereof.

The image capturing device 2 further comprises an illumination device orsection 6, suitable for projecting an illumination beam T towards thesubstrate S.

The reader 1 further comprises a processing and/or control device 7,capable of extracting the information content from the image captured bythe image capturing device 2 or by a portion thereof, for example thedecoding the two-dimensional code C, as well as of controlling the othercomponents of the reader 1.

The processing and/or control device 7 is per se well known andcomprises hardware and/or software means for treating the signal emittedby the sensor 4, such as filters, amplifiers, samplers and/orbinarizers, modules for reconstructing and/or decoding optical codes,including modules for consulting a table of possible codes, models forconsulting a table of whatever plaintext information associated with thepossible codes, optical character recognition modules, etc.

The acquired images and/or processings thereof, as well as theprogramming codes of the reader 1, processing parameter values and saidlook-up tables, are typically saved in digital form in at least onetemporary and/or mass memory device 8, possibly removable, of the reader1. The memory device 8 is also used as service memory to executesoftware algorithms.

The reader 1 can further comprise a communication device or interface 9,for communicating the acquired image and/or the extracted informationcontent outside of the reader 1 and/or per for entering configurationdata for the reader 1, coming from an external source.

The reader 1 further comprises at least one output device 10, fordisplaying to the user alphanumerical and/or graphical informationrelative for example to the operating state of the reader 1, to thecontent of the information read, etc., and/or for displaying the imagecurrently framed by the sensor 4. The output device 10 can,alternatively or additionally, comprise a printer, a voice synthesiseror other output devices of the aforementioned information.

The reader 1 further comprises at least one manual input device 11 ofcontrol signals and/or data, for example for configuring the reader,like for example a keyboard or a plurality of buttons or control levers,directional buttons, a mouse, a touch-pad, a touch screen, a voicecontrol device etc.

The reader 1 further comprises at least one power supply device 12 forthe various components with suitable voltage and current levels, with abattery source, or by taking a power supply signal from the electricalmains or from an external device.

The reader 1 further comprises a driver 13 of the illumination device 6,better described hereinafter.

The driver 13 and the illumination device 6 preferably implement, asbetter described hereinafter, besides the illumination function of thesubstrate S or of one or more regions of interest (ROI) thereof in orderto capture the image by the image forming device 3, also one or more ofthe following: an aiming device, an outcome indication device, a devicefor detecting the presence of a substrate S and/or for opticallymeasuring or estimating the reading distance and/or the focussingcondition of the image capturing device 2 (rangefinder).

The processing and/or control device 7 can be implemented by one or moreprocessors, in particular one or more microprocessors ormicrocontrollers, and/or circuits with discrete or integratedcomponents.

Similarly, the driver 13 can be implemented by one or more circuits withdiscrete or integrated components and/or by one or more processors, inparticular one or more microprocessors or microcontrollers.

Moreover, although in FIG. 2 the processing and/or control device 7 andthe driver 13 are shown as separate; they can share one or more of suchcircuits and processors, and/or the or one or more devices implementingthe memory means 8.

More generally, it should be understood that FIG. 2 illustrates distinctblocks from the functional point of view. From the physical point ofview, the various components of the reader 1 described above can be madein distinct objects, provided that they are in communication with eachother as schematically illustrated in FIG. 2, for the communication ofcontrol, data and/or power supply signals. The connection can be viacable and/or wireless.

Thus, the reader 1 described above can be made as a single object,wherein the various components are housed in a casing, not shown, havingsuitable shape and size for example for use in a fixed or portablestation; said casing comprises at least one transparent region for thepassage of the emitted light T and of the received light R. The casingand/or one or more internal supports are also configured to support thecomponents of the image capturing device 2 and of the illuminationdevice 6 in a predetermined mutual relationship.

Vice-versa, the output device 10 and/or the manual input device 11and/or the processing and/or control device 7 could be implemented atleast in part from a computer.

Furthermore, the illumination device 6 and the image forming device 3can be made in separate casings, each with its own transparent region,and be constrained in space in a predetermined mutual relationshipduring the installation step of the reader or reading system 1.

FIG. 3 illustrates in greater detail, though schematically, the imagecapturing device 2 according to an embodiment of the present invention.

The sensor 4 of its image forming device 3 comprises an array ofphotosensitive elements 14, each of which provides an electrical signalthe intensity of which is a function of the light striking it. As anexample, FIG. 3 shows a square two-dimensional sensor 4, but it can alsobe rectangular, round or elliptical. The sensor 4 can, for example, bemade in C-MOS or CCD technology. Optionally, the sensor 4 can be drivento extract the signal generated by a subset of its photosensitiveelements 14, and as a borderline case, each individual photosensitiveelement 14 can be individually driven.

The receiver optics 5 of the image forming device 3 of the imagecapturing device 2 is designed to form on the sensor 4 an image of thesubstrate S containing the optical information C, or of a regionthereof. The receiver optics 5 can comprise one or more lenses, one ormore diaphragms, refractive, reflective or diffractive optical elements,possibly anamorphic to modify the effective aspect ratio of the sensor4. As an example, in FIG. 3 the receiver optics 5 is shown as aninverting lens lying in a plane parallel to the sensor 4, and coaxialtherewith.

The image forming device 3 defines a working space region 15 extendingin front of the sensor 4. The working space region 15 is the region ofspace in which optical information C is correctly framed by the sensor 4and the image of which is sufficiently focused on the sensor 4. Withinsuch working space region 15, the optimal focal plane can be fixed ormade variable through an autofocus system. In the case represented of asquare sensor 4 as a particular case of a rectangular sensor, theworking space region 15 is pyramid- or frustum of pyramid-shaped; in thecase of a round or elliptical sensor 4, the working space region 15 is acone or a frustum of cone; in the case of a one-dimensional sensor 4 thebase of the pyramid becomes substantially thinner and the working region15 can be considered to be substantially flat.

The image forming device 3 further defines an optical axis of thereceiver optics 5, in short reception axis Z. The reception axis Z isdefined by the centres of the elements of the receiver optics 5, or bythe centres of curvature of the optical surfaces in the case of a singlelens. As will become clear hereinafter, the reception axis Z is notnecessarily perpendicular to the sensor 4, nor does it necessarily passthrough the centre of the sensor 4.

Especially in the case in which the reception optics 5 comprisesdeflecting elements, the reception axis Z may be non-rectilinear insidethe image forming device 3, but within the meaning of to the inventionit can in any case be modelled by a rectilinear reception axis Z.

Along the reception axis Z the vertex O of the working space region 15,in short the reception vertex O, is arranged. The vertex O of theworking space region 15 is the vertex of the pyramid or cone, and in thecase of inverting receiver optics 5 it falls in the optical centrethereof, while in the case of non-inverting receiver optics 5 ittypically falls behind the sensor 4.

The image forming device 3 further defines the angular width of theworking region 15 about the reception axis Z, which is typicallyexpressed in terms of four angles β₁, β₂, β₃, β₄ having origin in thereception vertex O and one of the sides coinciding with the receptionaxis Z, and extending in four half-planes that are perpendicular to eachother. With reference to the two main directions of the sensor 4, namelythe row and column directions of its photosensitive elements 14, it ispossible to speak of a “horizontal” field of view expressed by theangles β₁, β₃, and of a “vertical” field of view expressed by the anglesβ₂, β₄. In the particular case in which the sensor 4 is coaxial andcentred with respect to the receiver optics 5, the working space region15 has a symmetry and β₁=β₃ and β₂=β₄ in absolute value. In the case ofa one-dimensional sensor, the “vertical” field of view is much smallerthan the “horizontal” one, and can be substantially neglected.

The image forming device 3 further defines a depth of field DOF, whichexpresses the extent of the working space region 15 along the receptionaxis Z.

In FIG. 3, the substrate S at a generic reading distance D is indicatedwith S, and the region correspondingly framed by the sensor is indicatedwith 16; as particular cases the substrate S at the minimum possiblereading distance D₁ is indicated with S₁, and the region framed by thesensor is indicated with 16 ₁, while the substrate S at the maximumpossible reading distance D₂ is indicated with S₂, and the region framedby the sensor is indicated with 16 ₂. The depth of field is thereforegiven by DOF=D₂−D₁.

It is worth emphasising that the reading distances D, D₁, D₂ aremeasured along the reception axis Z from the reception vertex O, even ifthe reception axis Z is not necessarily perpendicular neither to thesensor 4 nor to the region 16 of the substrate framed by the sensor 4.

The working space region 15 can be fixed or made dynamically variable insize and/or in proportions through well known zoom and/or autofocussystems, such as electromechanical, piezoelectric or electro-opticalactuators for moving one or more lenses or diaphragms, mirrors or othercomponents of the receiver optics 5, and/or for changing the curvatureof one or more lenses, such as liquid lenses or deformable lenses and/orfor moving the sensor 4. In a preferred embodiment the receiver optics 5comprises an Arctic 416 SL-C1 liquid lens, manufactured by Varioptic SA,France.

In other words, while in FIG. 3 for the sake of simplicity it is assumedthat the field of view β₁, β₂, β₃, β₄ is equal at the various readingdistances D, this can be made variable along the reception axis Zthrough zoom systems, so that the working region 15 is no longer astatic frustum of pyramid or cone, rather has variable size and/orproportions. The description of the invention in any case remainstotally valid.

The illumination device 6 of the image capturing device 2 of theimager-type optical information reader 1 comprises an array 17 ofadjacent light sources 18. In FIG. 3, for the sake of clarity, only someof the light sources 18 are shown.

The light sources 18 of the array 17 can be individually driven, by thedriver 13, to be switched on and off, and preferably also in theintensity and/or in the wavelength, or range of wavelengths, ofemission. Therefore, this is what is defined in the field as a“pixelated source”, or that can be defined as PPEA (programmablephotonic emitter array).

The light sources 18 of the array 17 preferably each comprise a singleilluminating element, the illuminating elements being identical to oneanother in shape and size. However, the light sources 18 of the array 17can also comprise illuminating elements of different shape and/or size.Furthermore, the light sources 18 of the array 17 can each compriseplural illuminating elements collected into groups of a same or adifferent shape and/or size. In other words, the driving of thepixelated source can take place at the level of clusters of illuminatingelements or pixels, provided that the number of clusters, in other wordsof light sources 18 individually drivable according to the invention, isstill sufficiently large to implement the functionalities describedbelow of the illumination device 6.

The illumination device 6 optionally comprises an illumination optics.

The illumination optics can comprise one or more lenses and possiblediaphragms, refractive, reflective or diffractive optical elements,possibly anamorphic, common to all of the light sources 18 of the array17. The illumination optics can be a common and image inverting optics19 a, which as an example in FIG. 3 is shown coaxial with the array 17.

The illumination optics can also, as an alternative or additionally,comprise a plurality of lenses 19 b, each associated with a light source18 of the array 17, as better described as an example in FIGS. 14-16described hereinbelow. Such lenses 19 b, of comparable size to that ofthe light sources 18 or of their illuminating elements, have thefunction of determining and in particular of reducing the effectiveemission angle of the individual light source 18, and they can also havethe function of determining the orientation of the illumination beamemitted by the individual light source 18.

Each lens 19 b can be replaced by or associated with other opticalelements, such as diaphragms, prismatic surfaces, light guides orgradient index lenses, in order to better select the direction of thebeam emitted by the individual source, for example as described in theaforementioned EP 1 764 835 A1.

The plurality of lenses 19 b can also be used in association with acommon, non-inverting imaging optics 19 c, as shown as an example inFIG. 16 described hereinbelow, or in association with a common,inverting imaging optics 19 a.

The light sources 18 of the array 17 are preferably made in the form ofan integrated circuit on a common substrate. Preferably, the lightsources 18 are also driven through an address bus with row and columnindexes.

Preferably, the fill factor, namely the ratio between the overall areaoccupied by the active surface of the light sources 18 (or of theplurality of lenses 19 b) and the total area of the substrate of theintegrated circuit on which the sources (lenses) are arranged, is high,preferably over 90%.

In an embodiment, the light sources 18 of the array 17 are microLEDs.The microLEDs are micro-emitters, made for example with gallium nitride(GaN) technology, with emitting area of larger linear size equal toabout 20 micrometres, but currently also down to 4 micrometres; withthis technology arrays 17 can be made containing thousands or tens ofthousands of light sources 18 in extremely small size (for example, aside of a few mm for an array of 512×512 illuminating elements) and withminimal costs and consumption. Such devices are also able to emit atdifferent wavelengths.

In an embodiment, the light sources 18 of the array 17 are OLEDs(Organic Light Emitting Diodes). An OLED is an opto-electronic deviceobtained by arranging a series of thin organic films between twoconductors. When an electric current is applied, a light flow isemitted. This process is called electrophosphorescence. Even with asystem of many layers, an array 17 of OLEDs 18 is very thin, currentlyless than 500 nanometres (0.5 thousandths of a millimetre) and down to100 nm. OLEDs consume very little power, requiring very low voltages(2-10 Volts). OLEDs can emit at different wavelengths in the visiblespectrum. OLEDs can also be arranged in very compact arrays, with adensity currently up to 740 illuminating elements per inch (pixel/inch),each of 15 square micrometres (“OLED/CMOS combo opens a new world ofmicrodisplay”, Laser Focus World, December 2001, vol. 37, issue 12,Pennwell Publications, available at the link“http://www.optoiq.com/index/photonics-technologies-applications/lfw-display/lfw-article-display/130152/articles/laser-focus-world/volume-37/issue-12/features/microdisplays/oled-cmos-combo-opens-a-new-world-of-microdisplay.html”;“Organically grown: Luminescent organic crystals and polymers promise torevolutionize flat-panel displays with possibilities for low-costmanufacture and more portability”, Laser Focus World, August 2001, vol.37, issue 8, Pennwell Publications, available at the link“http://www.optoiq.com/index/photonics-technologies-applications/lfw-display/lfw-article-display/113647/articles/laser-focus-world/volume-37/issue-8/features/back-to-basics/organically-grown.html”).OLEDs have a very wide emission angle, currently up to 160°. An array 17of OLEDs can also be deposited on flexible substrates and therefore takeon a curved configuration. An array 17 of OLEDS can also be formed sothat the emitting elements have different shapes and/or sizes.

In an embodiment, the light sources 18 of the array 17 are LEDs (LightEmitting Diodes). LEDs are photoemitting devices, with a greatest lineardimension of 50 microns, which can reach 350 microns and more; thesedevices can achieve a high efficiency, but at the expense of havinglarge chip size and of needing dissipation elements between each other,which make an array 17 thus formed somewhat bulky and with large emptyareas between one emitter and the other, i.e. with a low fill factor;alternatively, LED emitters can be made on a substrate, as described forexample in the aforementioned document U.S. Pat. No. 5,319,182, forexample a C-MOS substrate, but with lower efficiency. Moreover, thedriver chips of LEDs 18 tend to have a contact at the centre thatproduces a shading at the centre of the area respectively illuminated.Even if there are ways to avoid this drawback, like for example thecontact geometries proposed in the aforementioned U.S. Pat. No.6,811,085, these systems are relatively expensive and consume arelatively large amount of energy, besides often needing a rather largedissipation area near to each source 18, which reduces its fill factor,as stated above.

In an embodiment, the light sources 18 of the array 17 are lasers,associated with micromirrors made in MEMS (MicroElectroMechanicalSystem) technology, that can be moved into an orientation such as not toallow light to pass, in other words switching it off within the meaningof the invention, and into at least one orientation such as to allowlight to pass, in other words switching it on within the meaning of theinvention. Such devices are known in the field as “picoprojectors”. Itis possible to provide for a laser associated with each micromirror, oralso a single laser common to the micromirrors. The presence of movingparts however involves a certain amount of consumption and wear.

Other technologies can be used to make the array 17 of light sources 18.

As an example of an array 17 of light sources 18, FIG. 4 illustrates, ina greatly enlarged scale, a portion of an array 17 of microLEDs withpre-collimation lens 19 b on each light source 18.

The illumination device 6 is configured so that each light source 18 ofthe array 17 emits an elementary illumination beam, having an ownaverage direction of propagation in the space in front of theillumination device 6. The illumination device 6 is also configured sothat the areas illuminated on a substrate S by adjacent light sources 18of the array 17 are adjacent to one another and possibly slightlyoverlapping, to form an overall illumination beam, indicated with Thereinafter, the shape and size of which depends upon how many and whichlight sources 18 are currently switched on by the driver 13, as betterexplained hereinafter. The number of light sources 18 of the array 17 isselected so that the area overall illuminated on a substrate S by theillumination device 6 undergoes a sufficiently small percentage changewhen an individual light source 18 is switched on/off. Preferably, thepercentage change is less than or equal to 15%, more preferably lessthan or equal to 10%, even more preferably less than or equal to 5%.

FIG. 3 illustrates the illumination beam T₀ that would be emitted—apartfrom angular blur of the light sources at opposite extremes of the array17—by the illumination device 6 if all of the light sources 18 of thearray 17 were switched on.

The illumination device 6 defines an optical illumination axis A, whichis the average direction of such a maximum illumination beam T₀, beingan axis of symmetry thereof in at least one plane, and typically in twoperpendicular planes in the illustrated case of a two-dimensional array17.

In the case of common illumination optics 19 a, 19 c and array 17centred with respect to the optical axis of such a common illuminationoptics 19 a, 19 c, the illumination axis A is defined by the centres ofthe elements of the common illumination optics 19 a, 19 c, or by thecentres of curvature of the optical surfaces in the case of a commonsingle lens 19 a, 19 c. Especially in the case in which the illuminationoptics 19 a, 19 b, 19 c comprises deflecting elements, the illuminationaxis A may be non-rectilinear inside the illumination device 6, butwithin the meaning of the invention it can still be modelled by arectilinear illumination axis A.

In the represented case of a square or in general rectangulartwo-dimensional array 17, the maximum illumination beam T₀ is pyramid-or frustum of pyramid-shaped; in the case of a round or elliptical array17, the illumination beam T₀ is a cone or a frustum of cone; in the caseof a one-dimensional array 17 the base of the pyramid becomessubstantially thinner, having a thickness equal to the size of the areailluminated by the individual light source 18, and the maximumillumination beam T₀ can be considered to be substantially flat.

The illumination device 6 further defines an illumination vertex A₀,which is the vertex of such a pyramid or cone; in the case of common,inverting illumination optics 19 a, the illumination vertex A₀ coincideswith the optical centre thereof, while in the case of non-invertingillumination optics 19 b, 19 c it typically falls behind the array 17.

It is worth emphasising that, depending on the orientation andpositioning of the common illumination optics 19 a, 19 c with respect tothe array 17 and/or on the geometry of the individual lenses 19 bassociated with the light sources 18, as shall become clear hereinafterthe illumination axis A is not necessarily perpendicular to the array17, nor does it necessarily pass through the centre of the array 17.

According to the invention, the illumination axis A does not coincidewith the reception axis Z. In particular, the illumination device 6 andthe image forming device 3 are not coaxial. In general, the receptionvertex O and the illumination vertex A₀ do not coincide and theillumination axis A and the reception axis Z are inclined with respectto each other. The illumination axis A and the reception axis Z can beparallel, provided that the reception vertex O and the illuminationvertex A₀ then do not coincide. The reception vertex O and theillumination vertex A₀ could in principle coincide, provided that theillumination axis A and the reception axis Z are then inclined withrespect to each other.

According to the invention, the driver 13 of the light sources 18 of thearray 17 is adapted, in the way described later on, to drive the lightsources 18 so as to switch off at least the light sources 18 thatilluminate outside of the boundary of the region 16 framed by the sensor4 on the substrate S at the generic reading distance D. Thus, in FIG. 3reference numeral 20 indicates the light sources 18 in the array 17 thatilluminate the boundary of the region 16 framed by the sensor 4 at thereading distance D. At the distance D, the driver 13 takes care ofswitching on the light sources 18 within the perimeter 20 inclusive, andof switching off those outside of the perimeter 20. In the case in whichit is wished to illuminate only a portion of the region 16 framed by thesensor 4, as better described hereinafter, the driver 13 will take careof switching on only a subset of the light sources 18 within theperimeter 20.

It is worth emphasising that, here and in the rest of the presentdescription and claims, by “switch off” and “switch on” and derivedforms it is not necessarily meant to indicate a switching of state,rather it is meant to encompass that, if a light source 18 is already inthe desired state, the driver 13 maintains such a state.

It is understood that under “boundary” of the region 16 framed by thesensor it is meant to indicate a layer across the geometric perimeterthereof, the thickness of which is determined by the area illuminated bythe individual light source 18 of the array 17, and therefore iscomparatively small with respect to the entire region 16 framed by thesensor 4.

As particular cases, in FIG. 3 reference numeral 20 ₁ indicates thelight sources 18 in the array 17 that illuminate the boundary of theregion 16 ₁ framed by the sensor 4 at the minimum reading distance D₁,at which the driver 13 takes care of switching on at most all of thesources within the perimeter 20 ₁ inclusive, and of switching off thoseoutside of the perimeter 20 ₁; reference numeral 20 ₂ indicates thelight sources 18 in the array 17 that illuminate the boundary of theregion 16 ₂ framed by the sensor 4 at the maximum reading distance D₂,at which the driver 13 takes care of switching on at most all of thesources within the perimeter 20 ₂ inclusive, and of switching off thoseoutside of the perimeter 20 ₂.

As can be seen from FIG. 3, the shifting within the array 17 of theperipheral switched-on sources 20 ₁, 20 and 20 ₂ as the reading distanceD changes between D₁ and D₂ allows the parallax error and theperspective distortion error inherent to the non-coaxial arrangement ofthe illumination device 6 with respect to the image forming device 3 tobe corrected (in this specific case the axis A also being inclined withrespect to the axis Z, hence the trapezoidal shape of the regions 20, 20₁, 20 ₂). Reference numerals 21, 21 ₁, 21 ₂ illustrate the perimeters ofthe region that would be illuminated, respectively at the distances D,D₁ and D₂, if all of the light sources 18 of the array 17 were switchedon, in other words the intersections of the maximum illumination beam T₀with the substrate S, S₁, S₂ at the various distances D, D₁, D₂: itshould be noted how each of such maximum illumination regions 21, 21 ₁,21 ₂ extend well beyond the region 16, 16 ₁, 16 ₂ framed by the sensor 4at the corresponding distance, which would correspond to a waste ofenergy, as well as bring about drawbacks in terms of deceiving visualindication to the user of the region 16, 16 ₁, 16 ₂ framed by the sensor4, in the case in which the light emitted by the light sources 18 is inthe visible spectrum.

Although it is not totally clear from FIG. 3, the optical paths betweenthe individual sources 18 of the array 17 that are switched on, thecommon illumination optics 19 a, 19 c where present, and the region 16,16 ₁, 16 ₂ framed by the sensor 4 on the substrate S, S₁, S₂ are notconstant. As a result of this there is a disuniformity of illuminationand/or loss of focus, schematically represented in FIG. 5.

Such a disuniformity of illumination and/or loss of focus can becorrected through a suitable design of the illumination optics 19 a, 19b, 19 c, that may however turn out to be particularly burdensome.

Alternatively or additionally, the driver 13 can drive the light sources18 so that they emit with different intensity, in particular increasinggoing from right to left in FIG. 3.

It is worth emphasising that, by modulating the intensity of theindividual light sources 18, it is also possible to correct possibledisuniformities in intensity of the sources 18 themselves, thusincreasing the insensitivity of the illumination device 6 to productiontolerances. In other words, it is not necessary to have a uniformemitter array 17.

Still alternatively or additionally, the array 17 of light sources 18can be arranged on a curved surface—which substantially becomes a curvedline in the case of a one-dimensional array—, corresponding to theoptimal focus curve (caustic) of the common illumination optics 19 a, 19c, so that the outermost light sources 18 of the array 17 are brought tothe correct distance by the common illumination optics 19 a, 19 c, so asto project a focused image onto the substrate S. An embodiment with acurved array 17 is schematically illustrated in FIG. 6 and is possiblein particular in the case of OLEDs. In an embodiment, the light sources18 of the array 17 can be arranged on a curved surface with the oppositeconcavity to that of FIG. 6. In this case, the illumination beams of theindividual light sources 18 diverge and the illumination optics can beabsent.

There are different methods according to which the driver 13 selectswhich light sources 18 of the array 17 to switch on, and optionally withwhat intensity and/or emission wavelength(s), as a function of thereading distance D within the depth of field DOF of the image formingdevice 3, in order to illuminate the entire and only the region 16framed by the sensor 4 on the substrate S. Hereinafter, for the sake ofbrevity reference shall be made only to the determining of the lightsources 18 to switch on, it being implicit that it is possible at thesame time to determine the respective intensity and/or emissionwavelength(s).

First, the determining can occur either run-time or one-off.

In the case of run-time determining, the driver 13 itself shall comprisehardware and/or software modules to implement the determining method. Asillustrated in FIG. 7, in a step 100 the current working distance Dwithin the depth of field DOF (D₁≦D≦D₂) is set or detected. In a step101 the subset 18 a of light sources 18 that must be switched on toilluminate the entire and only the region 16 framed by the sensor 4 isdetermined, in particular with one of the methods described below. In astep 102, at most all of the light sources of the subset 18 a areswitched on.

In the case of one-off determining a look-up table is built, to whichthe driver 13 then refers during the normal operation of the imagecapturing device 2 of reader 1. The driver 13 can again comprise saidhardware and/or software modules, or the method can be carried outthrough an external processor, and only the look-up table can be loadedin the memory 8 of the reader 1 associated with the driver 13. Theone-off determining preferably takes place substantially for eachreading distance D within the depth of field DOF, in other wordsvariable between D₁ and D₂ with continuity or with suitable sampling,and thus provides for a cycle of operations. The sampling range of theworking distances D may be non-constant, in particular the sampledworking distances D can be closer to each other near to the minimumworking distance D₁ and less close to each other near to the maximumworking distance D₂, where the configuration of light sources 18 to beswitched on changes more slowly. With reference to FIG. 8, in a step 103the working distance D is selected as the minimum working distance D₁,or the maximum working distance D₂, respectively. The step 101 ofdetermining the subset 18 a of light sources 18 that must be switched onto illuminate the entire and only the region 16 framed by the sensor 4is then carried out. In a step 104 a record is then stored in thelook-up table, comprising the selected working distance D (correspondingin this first execution of the cycle to D₁ or D₂, respectively) and thesubset 18 a determined in step 101. In a step 105 the working distance Dis then increased or decreased, respectively, by an infinitesimal amountor an amount based on the preselected sampling. In a step 106 it is thenchecked whether the cycle has been carried out over the entire depth offield DOF, in other words whether the working distance D exceeds themaximum working distance D₂, or is less than the minimum workingdistance D₁, respectively. In the negative case, steps 101, 104, 105 and106 are repeated, therefore inserting a new record in the look-up table.When the cycle has been carried out over the entire depth of field DOF,in other words when the check of step 106 is positive, the driver 13 canenter into normal use mode. In this mode, in step 100 the currentworking distance D within the depth of field DOF (D₁≦D≦D₂) is set ordetected. In a step 107 the subset 18 a of light sources 18 that must beswitched on to illuminate the entire and only the region 16 framed bythe sensor 4 at the current working distance D is read from the look-uptable. In step 102, at most the light sources of the subset 18 a areswitched on.

The step 101 of determining the subset 18 a of light sources 18 thatmust be switched on, at a given current working distance D within thedepth of field DOF, to illuminate the entire and only the region 16framed by the sensor 4 can be implemented, in different embodiments ofthe image capturing device 2, according to different methods, bothrun-time (step 101 of FIG. 7) and one-off (step 101 of FIG. 8).

A first method is of the analytical type. Once the geometric and opticalconfiguration of the image capturing device 2 has been established, itis indeed possible to calculate, for each reading distance D, whichlight source 18 of the array 17 illuminates the elementary area framedby each photosensitive element 14 of the sensor 4. It should be notedthat in practice the elementary area framed by each photosensitiveelement 14 of the sensor 4 can be illuminated at most by four lightsources 18 arranged adjacent to one another forming a square in thearray 17.

A preferred embodiment of analytical method is schematically illustratedin FIG. 9 and subsequently described in greater detail with reference toFIGS. 10 to 17.

With reference to FIG. 9, in a step 108, in a first reference systemassociated with the reception device 3, in particular originating in thereception vertex O, and based on the configuration of the image formingdevice 3, the coordinates of some peculiar points are calculated, whichallow the boundary of the region 16 framed on the substrate S by thesensor 4 to be identified. Such peculiar points are preferably thosewhose image is formed on photosensitive elements 14 that define theperimeter of the sensor 4 and/or on the central photosensitive element14 of the sensor 4. In particular, in the case of a rectangular orsquare sensor 4, the reference system is preferably Cartesian and thepeculiar points preferably correspond to those seen by thephotosensitive elements 14 at least at two opposite vertexes of thesensor 4; in the case of a circular or elliptical sensor 4, thereference system is preferably cylindrical and the peculiar pointspreferably correspond to the central photosensitive element 14 and to aperipheral photosensitive element 14, or to the two or four peripheralphotosensitive elements 14 along the axes of symmetry of the sensor 4.Indeed, there is an analytical relationship that expresses thecoordinates of all of the points corresponding to the perimeter of theregion 16 framed by the sensor 4 on the substrate S as a function ofsuch peculiar points.

In a step 109 a transformation of the coordinates of the peculiar pointsinto a second reference system, associated with the illumination device6 and in particular originating in the illumination vertex A₀, iscarried out. In particular, in the case of a rectangular or square array17, the second reference system is preferably Cartesian; in the case ofa circular or elliptical array 17, the second reference system ispreferably cylindrical. In some cases, it may be suitable to change,increase or decrease the peculiar points passing from one referencesystem to another and using the analytical relationships that expressthe coordinates of all of the points corresponding to the perimeter ofthe region 16 framed by the sensor 4 on the substrate S and/or thatexpress the coordinates of all of the points corresponding to theperimeter of the region to be illuminated on the substrate by the array17: for example, if the region 16 framed by the sensor 4 on thesubstrate S is a rectangle and is seen as a trapezium by theillumination device 6, it is possible to operate on the four vertexes,or it is possible to operate for example on two opposite vertexes or onthe centre and one vertex in the first reference system, and to passthrough the analytical expression of the rectangle to obtain the fourvertexes of the trapezium in the second reference system.

In a step 110, in the second reference system and based on theconfiguration of the illumination device 6, the light sources 18 of thearray 17 that illuminate the corresponding peculiar points arecalculated.

The transformation of coordinates between two reference systems, carriedout in step 109, is per se well known. Purely as an example, withreference to FIG. 10, in the case in which the first reference system isa Cartesian system X,Y,Z having origin in the reception vertex O and thesecond reference system is a Cartesian system U,V,W having origin in theillumination vertex A₀, the transformation of coordinates is in generala rototranslation (rotation plus translation), which can be reduced to arotation or to a translation in particular cases. Indicating thecoordinates of the illumination vertex A₀ of the second reference systemin the first reference system with x₀,y₀,z₀, and the direction cosinesof the axes U,V,W of the second reference system with respect to thefirst reference system X,Y,Z with cos α₁ . . . cos α₉ (the angles α₁ . .. α₉ are indicated with respect to a reference system U′,V′,W′translated in O in FIG. 10 for clarity of representation), saidtransformation is expressed by the following set of relationships:

u=(x−x ₀)*cos α₁+(y−y ₀)*cos α₂+(z−z ₀)*cos α₃  (1)

v=(x−x ₀)*cos α₄+(y−y ₀)*cos α₅+(z−z ₀)*cos α₆  (2)

w=(x−x ₀)*cos α₇+(y−y ₀)*cos α₈+(z−z ₀)*cos α₉  (3)

The position of the illumination vertex A₀ is illustrated in the firstquadrant (positive values of x₀, y₀, z₀), but it can be in any quadrant.The illumination vertex A₀ can also lie along one of the axes and/or atthe reception vertex O. Moreover, one or more of the direction cosinescos α₁ . . . cos α₉ can be zero or unitary in the case in which one ormore axes of the two reference systems are parallel and/or coincide orare perpendicular.

With the aid of FIGS. 11 and 12, the relationship that correlates thepoints of the region 16 framed by the sensor 4 on the substrate S withthe photosensitive elements 14 shall now be explained, said relationshipbeing used in step 108 of the method of FIG. 9, in the case oftwo-dimensional rectangular—or square as a special case—sensor 4 andinverting optics, schematised as a single paraxial lens 5, having themain plane—which in the specific case is the plane perpendicular to thereception axis Z passing through the optical centre of the receiveroptics 5—parallel to the plane of the sensor 4. It should be noted that,in order to remain in general terms, the reception axis Z does not passthrough the centre of the sensor 4, rather through a generic point O_(s)thereof.

In the case of such an embodiment of the image forming device 3, thefirst reference system is advantageously selected as a Cartesianreference system X,Y,Z, having origin in the reception vertex O, axis Zselected to coincide with the reception axis Z, but oriented theopposite way to the path of the reception light R, and axes X, Yoriented parallel to the main directions of the sensor 4, namely thecolumn and row directions of its photosensitive elements 14.

At the generic working distance D, namely in the plane having theequation

z=D  (4),

the working space region 15 (indicated with a dotted and dashed line)defines the region 16 framed by the sensor 4 on the substrate S (notshown for the sake of clarity).

The angles β₁, β₂, β₃, β₄ that define the field of view on the side ofthe substrate S are correlated to the angles β′₁, β′₂, β′₃, β′₄, on theside of the sensor 4 in opposite quadrants, between the reception axis Zand the edges of the sensor 4 by the following relationship:

β′_(k)=AMAG_(S)*β_(k)  (5)

where AMAG_(S) is the angular magnification of the receiver optics 5,generally AMAG_(S)≦1.

As stated above, although the field of view β₁, β₂, β₃, β₄ is shown asconstant along the reception axis Z, this is not in general necessary,in the case for example of zoom and/or autofocus systems, in which therecan be fields of view which are a function of the working distance,namely of the current z coordinate. In the above formula (5) and in thefollowing ones illustrated below, in this case the values of the fieldof view at the considered working distance D will be used.

If s is the distance between the sensor 4 and the main plane of thereceiver optics 5, the reception axis Z meets the sensor 4 at a pointO_(s) of coordinates (0,0,s). With reference to FIG. 12, if the pointO_(s) falls at the centre of a photosensitive element 14 thereof, and ifI and J are the column and row inter-axis spacing of the sensor 4,namely the distances between the centres of two adjacent photosensitiveelements 14 along the row direction and column direction, respectively,each photosensitive element 14 is defined by its centre, havingcoordinates in the reference system X,Y,Z expressed by the followingrelationship:

F(i*I,j*J,s)  (6)

where i and j are the column and row indexes of the sensor 4,respectively, which can take on positive and negative integer values,and take on zero value at the photosensitive element 14 centred atO_(s).

If the point O_(s) were not to fall at the centre of a photosensitiveelement 14, rather a distance I₁,J₁ from the centre, the coordinates ofthe centre of each photosensitive element would be expressed by(i*I+I₁,j*J+J₁,s). If the photosensitive elements 14 of the sensor 4were not the equal to each other, it would still be possible tocalculate the coordinates thereof in the reference system X,Y,Z. Itshould be noted that the column and line inter-axis spacing I,J of thesensor 4 are equal to each other in the case of square or circularphotosensitive elements uniformly spaced on the sensor 4.

If the point O_(s) falls at the centre of the sensor 4, the receptionaxis Z is an axis of symmetry for the sensor 4 and the working spaceregion 15 has two planes of symmetry, for which reason β₁=β₃ and β₂=β₄.In this case, the column index, as well as the row index, has extremevalues that are equal in absolute value.

It can easily be recognized that the centre P of the region framed bythe generic photosensitive element 14, defined by indexes i,j, atdistance D has coordinates expressed by the following relationships:

$\begin{matrix}{x = {{x(j)} = {D*\tan \left\{ {\frac{1}{AMAGs}*{\arctan \left( \frac{j*J}{s} \right)}} \right\}}}} & (7) \\{y = {{y(i)} = {D*\tan \left\{ {\frac{1}{AMAGs}*{\arctan \left( \frac{i*I}{s} \right)}} \right\}}}} & (8) \\{z = D} & (9)\end{matrix}$

In the case of unitary angular magnification AMAG_(S)=1, therelationships (7), (8) reduce to simple proportions:

$\begin{matrix}{x = {{x(j)} = {D*\left( \frac{j*J}{s} \right)}}} & (10) \\{y = {{y(i)} = {D*\left( \frac{i*I}{s} \right)}}} & (11)\end{matrix}$

In the case of the embodiment illustrated in FIG. 11, in step 108 of themethod of FIG. 9 the relationships (7), (8), (9) or (10), (11), (9),respectively, are applied to the four points P₁, P₂, P₃, P₄ defining thevertexes of the region 16 framed by the sensor 4 on the substrate S, orelse even only at the opposite vertices P₁ and P₃ o P₂ and P₄.

Although not used in the method of FIG. 9, it is worthwhile illustratingthe following relationships, the inverses of relationships (7), (8) andwherein the working distance D is replaced by the generic coordinate z:

$\begin{matrix}{j = {{j\left( {x,z} \right)} = {\frac{s}{J}*\tan \left\{ {{AMAGs}*{\arctan \left( \frac{x}{z} \right)}} \right\}}}} & (12) \\{i = {{i\left( {y,z} \right)} = {\frac{s}{I}*\tan \left\{ {{AMAGs}*{\arctan \left( \frac{y}{z} \right)}} \right\}}}} & (13)\end{matrix}$

that allow, given any point P of the working space region 15, theindexes of the photosensitive element 14 of the sensor 4 that receivesits image to be identified. Of course, since the indexes i,j are integernumbers, the relationships will be approximated to the nearest integernumber. In the case of slightly overlapping fields of view of theindividual photosensitive elements 14, in the overlapping areas the twointeger numbers approximated by defect and by excess will identify thepair of photosensitive elements 14 that receive the image of the pointbeing considered.

It is straightforward to recognize that what has been outlined withreference to FIGS. 11 and 12 holds true, mutatis mutandis, for anembodiment of the illumination device 6 with rectangular—or square as aspecial case—two-dimensional array 17 and common, inverting illuminationoptics 19 a, having the main plane—that in this particular case is theplane perpendicular to the optical axis of the illumination optics 19 apassing through the optical centre of the illumination optics 19 aitself—parallel to the plane of the array 17. The related references areindicated between brackets in FIGS. 11 and 12. The point G indicates theposition of the virtual light source that illuminates the point P, towhich corresponds at least one light source 18 of the array 17, and atmost four light sources 18 adjacent to one another forming a square.

In the case of such an embodiment of the illumination device 6, thesecond reference system is advantageously selected as a Cartesianreference system U,V,W, having origin in the illumination vertex A₀,with axis W coinciding with the optical axis of the common, invertingillumination optics 19 a and axes U, V oriented parallel to the maindirections of the array 17, namely the row and column directions of itslight sources 18. It should be noted that the axis W coincides with theillumination axis A only in the particular case in which it passesthrough the centre of the array 17.

Once the coordinates u,v,w of the generic point P in the system U,V,W,or rather of the peculiar points P₁, P₂, P₃, P₄ or P₁, P₃ o P₂, P₄, havebeen obtained in step 109 of the method of FIG. 9 and through therelationships (1), (2), (3), in step 110 of the method of FIG. 9 thefollowing relationships will therefore be applied to such coordinates:

$\begin{matrix}{n = {{n\left( {u,w} \right)} = {\frac{t}{N}*\tan \left\{ {{AMAGa}*{\arctan \left( \frac{u}{w} \right)}} \right\}}}} & (14) \\{m = {{m\left( {v,w} \right)} = {\frac{t}{M}*\tan \left\{ {{AMAGa}*{\arctan \left( \frac{v}{w} \right)}} \right\}}}} & (15)\end{matrix}$

The relationships (14), (15), corresponding to the relationships (12),(13), allow the column and row indexes m, n of the light source 18 ofthe array 17 that illuminates point P to be calculated, where indexes0,0 are associated with the light source 18 lying along axis W (pointA₂).

In relationships (14), (15), M and N are the column and row inter-axesof the light sources 18, AMAG_(a) is any angular magnification of thecommon, inverting illumination optics 19 a, wherein the followingrelationship (16) holds true

γ′_(k)=AMAGa*γ_(k)  (16)

t is the distance between the plane of the array 17 and the illuminationvertex A₀, therefore measured along the axis W, and the generalizationsand the special cases discussed above with reference to the imagecapturing device 3 hold true.

In the embodiment of the illumination device 6 illustrated in FIG. 11,there can additionally be lenses 19 b associated with the individuallight sources 18 of the array 17, in order to modify the angularemission width and/or direction of emission thereof. Regarding this,reference shall be made to the subsequent description of FIGS. 14-16.

The relationships (14) and (15) express the correlation, to be used instep 110 of the method of FIG. 9, between any point P of the workingspace region 15 and the row and column indexes of the light source 18 ofthe array 17 that illuminates it also for an embodiment of theillumination device 6 with common, non-inverting illumination optics 19c, again having the main plane—which in this particular case is theplane perpendicular to the optical axis of the illumination optics 19 cpassing through the optical centre of the illumination optics 19 citself—parallel to the plane of the array 17, as shown in FIG. 13.

It should be emphasised that the relationships (1) to (16) areanalytical relationships that only depend on known (design) geometricparameters of the reader 1, and in particular of its image formingdevice 3 and of its illumination device 6, and/or of their relativespatial arrangements, including the relative spatial arrangements oftheir components or subassemblies.

The relationships (14) and (15) hold true also in the case in which thenon-inverting-type illumination optics comprises the aforementionedplurality of lenses 19 b associated with the individual light sources 18of the array 17, possibly in association with a common non-invertinglens 19 c, as illustrated in FIGS. 14-16.

For the sake of simplicity, an illumination device 6 having such lenses19 b is illustrated in FIG. 14 in a plane that is assumed to contain oneor the main direction of the array 17 and the illumination axis A,believing that such a figure is sufficiently descriptive of the moregeneral three-dimensional case in the light of the previous teachings.

Each individual lens 19 b addresses the light emitted by the lightsource 18 on which it is placed so as to form a beam that emits withinan angle ω_(m) determined by the size of the lens 19 b, centred aroundits own illumination axis A_(m) determined by the line joining thecentre of the light source 18 and the centre of the lens 19 b associatedtherewith. By suitably positioning the centre of the lens 19 b withrespect to the light source 18 it is therefore possible to ensure thatthe individual illumination axis A_(m) is inclined by a desired anglewith respect to the plane of the array 17.

In the embodiment of FIG. 14, the illumination axes A_(m) diverge fromeach other to define the illumination vertex A₀—which in the case shownfalls behind the array 17—and uniformly radially spaced by an angle μ.In this case, the illumination axis A of the illumination device 6 isthe bisector of the angle defined by the illumination axes of the firstand of the last source, and it is perpendicular to the plane of thearray 17. Nevertheless, by suitably orienting the lenses 19 b withrespect to the light sources 18, it would be possible to have theelementary beams cross in front of the array 17. In the caseillustrated, the emission angles ω_(m) are all equal to angle μ, forwhich reason adjacent light sources 18 illuminate adjacent contactingareas 22 _(m), however the emission angles ω_(m) can be slightly greaterthan angle μ so that the illuminated areas 22 _(m) slightly overlap.

The embodiment of FIG. 15 differs from that of FIG. 14 in that theillumination axis A is not perpendicular to the plane of the array 17,rather inclined by an angle η₀ with respect to the normal to the planeof the array 17.

These embodiments of illumination device 6 have the advantage of havinga very low thickness in the direction perpendicular to the plane of thearray 17.

In both cases, in order to reduce the size of the emitted beam it issufficient to place a lens with angular magnification <1, and preciselywith an angular magnification AMAGm=ω₁/ω, in front of each light source18, which will emit within its native angle ω.

The embodiment of the illumination device 6 of FIG. 16 differs from thatof FIG. 14 in that downstream of the array 17 and of the individuallenses 19 b, a further common, non-inverting optics 19 c is arranged,having angular magnification factor AMAGm<1 to further reduce theemission angle of the individual light sources 18, to a valueω′_(m)=AMAGm*ω_(m). The thickness of the illumination device 6 in thedirection perpendicular to the plane of the array 17 increases, but thecollimation of the illumination beam T is more progressive. In the caseof light sources 18 having a particularly small native emission angle w,the angular magnification factor AMAGm could be AMAGm>1. A similarcommon, non-inverting optics 19 c can also be provided for in the caseof the embodiment of FIG. 15.

In the embodiments of FIGS. 14-16, the illumination axes A_(m), theemission angles ω′_(m), and the angular magnification factors AMAGm ofthe individual light sources 18 can be different to one another, andsimilarly the illumination axes A_(m) do not necessarily have to beequally spaced, even if with a correlated complication of the method ofdetermining (step 101) the light sources 18 of the array 17 to beswitched on. However, given an illumination device 6, the angles thatthe individual illumination axes of the light sources 18 form with theillumination axis A can in any case be calculated or measured.Therefore, it is always possible to determine a function, howevercomplex it might be, that correlates a point P on the substrate S with alight source 18 of the array 17 that illuminates it.

In FIGS. 14 to 16 the regions 22 _(m) illuminated by the light sources18 are shown purely for illustrative purposes on a plane parallel to theplane of the array, which however is not necessarily a plane at a givenreading distance D, nor is necessarily a plane of focus or of equalblurring of the image forming device 3.

FIGS. 11 and 13-16, as well as FIG. 17 described hereinafter, can beconsidered as representing as many embodiments of the illuminationdevice 6 wherein the array 17 is curved (FIG. 6).

It is straightforward to recognize that what has been outlined withreference to FIGS. 13-16 holds true, mutatis mutandis, for correspondingembodiments of the image forming device 3. The relative referencenumerals are not indicated within brackets in FIGS. 13-16 for the sakeof brevity.

With the aid of FIG. 17 the relationship that correlates the points ofthe region 16 framed by the sensor 4 on the substrate S with thephotosensitive elements 14 of the sensor 4 shall now be explained, saidrelationship being used in step 108 of the method of FIG. 9, in the caseof a rectangular—or square as a special case—two-dimensional sensor 4and inverting optics, schematised as a single paraxial lens 5, havingthe main plane—that in this specific case is the plane perpendicular tothe reception axis Z passing through the optical centre of the receiveroptics 5—not parallel to the plane of the sensor 4.

In the case of such an embodiment of the image forming device 3, thefirst reference system is advantageously selected as a Cartesianreference system X,Y,Z, having origin in the reception vertex O, axis Zselected so as to coincide with the reception axis Z but oriented theopposite way to the path of the reception light R (FIG. 2), and axis Yoriented parallel to the row direction of the sensor 4, according towhich the photosensitive elements 14 are indexed by index i. The columndirection of the sensor 4, according to which the photosensitiveelements 14 are indexed by index j, forms an angle δ with axis X. Thecase in which the main plane of the receiver optics 5 is also inclinedwith respect to the row direction of the sensor 4 is a generalisationthereof, that is not dealt with for the sake of brevity. Moreover, inFIG. 17 the reception axis Z is, for the sake of simplicity, indicatedas passing through a point O_(s) of the sensor 4 corresponding to thecentre of the sensor 4, and in particular through the centre of aphotosensitive element 14 thereof, however in general this is notstrictly necessary and the considerations outlined with reference toFIG. 12 hold true.

The plane 30 (schematically indicated by three dotted lines) on whichthe sensor 4 lies meets the plane X,Y along a straight line 31 definedby the set of equations

x=−s/tan δ  (17)

any y  (18)

z=0  (19)

where the minus sign in relationship (17) takes the fact that thedistance s between the reception vertex O and the intersection O_(s) ofthe reception axis Z with the sensor 4 is negative in the referencesystem X,Y,Z into account.

At the generic working distance D within the depth of field DOF of theimage forming device 3, measured along the reception axis Z and definedby the point Q of the reception axis Z of coordinates

Q(0,0,D)  (20),

the plane 32 (also schematically indicated by three dotted lines)passing through the straight line 31 and through the point Q is defined,and therefore can be expressed through the following relationship:

x*D+z*(−s/tan δ)−[(−s/tan δ)*D]=0  (21)

With the conventions used above with reference to FIG. 12, eachphotosensitive element 14 of the sensor 4 is defined by its centre,having coordinates in the reference system X,Y,Z expressed by thefollowing relationship (22):

F(j*J*cos δ,i*I,s+j*J*sin δ)  (22)

written assuming, for the sake of simplicity, a unitary angularmagnification AMAG_(S) of the receiver optics 5. In this hypotheticalcase, the centre of the region framed by the generic photosensitiveelement 14 identified by the indexes i,j, lies on the straight linepassing through the photosensitive element 14 itself, and through thereception vertex O (straight line FOP of FIG. 17) and therefore can beexpressed through the following set of parametric equations:

x=j*J*cos δ*f  (23)

y=i*I*f  (24)

z=(s+j*J*sin δ)*f  (25)

with any f.

In the region 16 framed by the sensor 4 on the plane 32, the coordinatesof the centre P of the region framed by each photosensitive element 14are therefore expressed by the equations (23),(24),(25) for the value ofthe parameter f that is obtained by combining relationships(23),(24),(25) themselves with relationship (21), namely:

$\begin{matrix}{f = {- \frac{s*D}{\left\lbrack {j*J*\sin \; \delta*\left( {D - s} \right)} \right\rbrack - s^{2}}}} & (26)\end{matrix}$

In the case of the embodiment illustrated in FIG. 17, in step 108 of themethod of FIG. 9 relationships (23), (24), (25) with the value of f ofrelationship (26) are applied to the four points P₁, P₂, P₃, P₄ definingthe vertexes of the region 16 framed by the sensor 4 on the substrate S,or even only to the opposite vertices P₁ and P₃, or P₂ and P₄.

FIG. 17 and the previous description can also apply, mutatis mutandis,to the illumination device 6 in the case in which the latter has acorresponding embodiment, in other words with rectangular—or square as aspecial case—two-dimensional array 17 and inverting optics, having themain plane—that in this specific case is the plane perpendicular to theaxis of the illumination optics 19 a passing through the optical centreof the common illumination optics 19 a itself—not parallel to the planeof the array 17. Also in this case the relative reference numerals areput within brackets in FIG. 17.

Once the coordinates u,v,w in the system U,V,W of the generic point P,or better of the points P₁, P₂, P₃, P₄ or P₁, P₃ or P₂, P₄, have beenobtained, in step 109 of the method of FIG. 9 and through relationships(1), (2), (3), in step 110 of the method of FIG. 9 the followingrelationships will therefore be applied to such coordinates

n=u/(N*cos ε*f)  (27)

m=v/(M*f)  (28)

that are inverse to relationships (23), (24), where the value ofparameter f also satisfies the relationship

$\begin{matrix}{f = {- \frac{t*w}{\left\lbrack {n*N*\sin \; ɛ*\left( {w - t} \right)} \right\rbrack - t^{2}}}} & (29)\end{matrix}$

with

w=(t+n*N*sin ε)*f  (30)

where relationships (29) and (30) correspond to relationships (26) and(25).

By combining relationships (30) and (27), one obtains:

$\begin{matrix}{{{n\left( {u,w} \right)} = {\frac{u*t}{N}*\left( {{w\; \cos \; ɛ} - {u\; \sin \; ɛ}} \right)}};} & (31)\end{matrix}$

by replacing (31) in (29), f(u,w) is obtained, and finally by replacingthe latter value in (28), m(u,v,w) is found, which are omitted for thesake of brevity.

It should be emphasised that also the relationships from (17) to (31)are analytical relationships that only depend upon known (design)geometric parameters of the reader 1, and in particular of its imageforming device 3 and of its illumination device 6, and/or of theirrelative spatial arrangements, including the relative spatialarrangements of their components or subassemblies.

Said relationships therefore allow the row and column indexes m, n ofthe light source 18 of the array 17 that illuminates the peculiarpoints, and in general any point P of the working space region 15, to becalculated, wherein the indexes 0,0 are associated with the light source18 lying along axis W (point A₂), in the various configurations of theimage forming device 3 and of the illumination device 6.

It should be understood, as stated above with reference to FIG. 9, thatit might be necessary or advantageous to change/increase/decrease thepeculiar points in either reference system, according to the type offigure resulting in each of them. Therefore, relationships (1) to (3)and their inverses can be applied not only to peculiar points, ratheralso to expressions of lines or curves.

The formulae described above therefore allow the determining, accordingto the analytical method, of the subset 18 a of light sources 18 of thearray 17 to be switched on to illuminate the entire region 16 framed bythe sensor 4 on a substrate S at a given working distance D to becompleted, step 101 of the run-time or one-off method of FIG. 7 or ofFIG. 8.

The formulae described above can be simplified with particularconfigurations of the image capturing device 2. Moreover, differentreference systems may be equally or more advantageous, with theapplication of correspondingly different formulae.

In order to calculate the intensity with which to switch on each lightsource 18 of the array 17 determined in step 101 of the method of FIG. 7or of FIG. 8, in the case in which it is variable, it is easy tocalculate the distance d of every point P of the region 16 framed by thesensor 4 on the substrate S from the light source 18 that illuminates it(the distance d is not indicated in the figures for the sake ofclarity). In the cases of FIGS. 10-17 it is possible to easily expresssuch distances in the reference system U,V,W through the followingrelationship:

d=√{square root over ((u−nN)²+(v−mM)²+(w−t)²)}{square root over((u−nN)²+(v−mM)²+(w−t)²)}{square root over((u−nN)²+(v−mM)²+(w−t)²)}  (32)

where the magnitudes are taken with suitable signs.

For the purposes of the initial design of the array 17 of light sources18, it is worthwhile calculating what is the minimum solid angle withinwhich the array 17 must be able to emit in order to illuminate theentire working space region 15, namely the entire field of view of theimage forming device 3 within its entire depth of field DOF. In otherwords, the solid angle subtended by the maximum illumination beam T₀must be at least equal to such a minimum solid angle.

This can be easily carried out by applying the concepts and formulaedescribed above to the suitable peculiar points, for example to thevertexes of the working region 16 ₁ framed by the sensor S at theminimum reading distance D=D₁ and to the vertexes of the working region16 ₂ at the maximum reading distance D=D₂, and by evaluating which arethe most positive and most negative values obtained for the indexes mand n. One or more of the quantities indicative of the configuration andgeometry of the illumination device 6 and of its position with respectto the image forming device 3 are, in such an evaluation, advantageouslykept in parameter form. Such quantities include the coordinates x₀,y₀,z₀of the illumination vertex A₀ in the reference system X,Y,Z associatedwith the image forming device 3, the direction cosines cos α₁ . . . cosα₉, the distance t of the array 17 from the illumination vertex A₀, theangular magnification AMAG_(a) of the illumination optics, the angle ofinclinations in the case of the embodiment of FIG. 17, and also ingeneral the column and row inter-axes M and N, and the extremes of thecolumn and row indexes m, n of the array 17, in other words the numberof light sources 18 of the array 17, and the location of point A₂ withinthe array 17. The effective values of such quantities may be subject topossible design restrictions, such as the maximum size of the imagecapturing device 2 and the availability of arrays 17 having suitablecharacteristics. However, in general it is always possible to size andposition the array 17 in such a way that all of its light sources 18 areexploited, in other words switched on, at at least one reading distanceD. Similar considerations are valid in the case of designing of theentire image capturing device 2, when one or more of the quantitiesindicative of the configuration and geometry of the image forming device3 will also be maintained in parameter form, for example the distance sof the sensor 4 from the reception vertex O, the angular magnificationAMAG_(S) of the receiver optics 5, the angle of inclination 8 in thecase of the embodiment of FIG. 17, and also in general the column androw inter-axes I and J, and the extremes of the column and row indexesi, j of the sensor 4, in other words the number of photosensitiveelements 14 of the sensor 4, and the location of the point O_(s) withinthe sensor 4.

Nevertheless, it should be understood that the values of the quantitieslisted above are known constants for a given image capturing device 2.

From what has been outlined above simplified formulae can be derived, tobe applied in the case of one-dimensional sensor 4 and/or array 17,and/or formulae, in general more complex, to be applied in the case of acurved array 17 (FIG. 6).

It must also be clear that the substrate S can in practice have anyorientation with respect to the reception axis Z, provided that theoptical information C occupies an area in space that overall lies withinthe working space region 15, and at sufficiently similar localdistances, so that the focussing on the sensor 4 is sufficientlyuniform; in such conditions the illumination obtained by theillumination device 6 is also suitable in practice, even if calculatedbased on a single working distance D. A more accurate determination ofthe light sources 18 to be switched on, which takes such an inclinationinto account, can however be carried out, even if the formulae to beapplied according to the analytical case are more complex.

A second method for implementing, in different embodiments of the imagecapturing device 2, both run-time (FIG. 7) and one-off (FIG. 8), thestep 101 of determining the subset 18 a of light sources 18 that must beswitched on, at a given current working distance D within the depth offield DOF, in order to illuminate the entire and only the region 16framed by the sensor 4 is of the empirical or adaptive type, and anexemplary embodiment thereof is shown in FIG. 18.

This embodiment is well adapted to the case in which the plane of thesensor 4 and the plane of the array 17 are parallel, and they arerectangular. A more general method is described below.

The driver initially takes care of switching on all of the light sources18 of the array 17 in a step 120. In such a condition, the entire region16 framed by the sensor 4 is certainly illuminated, and this is checkedin a step 121. The negative case implies a design and/or assembly errorof the image capturing device 2—in other words the condition that themaximum illumination beam T₀ is greater than or equal to the minimumrequired solid angle is not met and/or the position of the illuminationvertex A₀ and/or the inclination of the illumination axis A with respectto the reception axis Z are not correct—and/or a malfunction of thearray 17, and consequently the method ends. Steps 120, 121 can howeverbe omitted.

In the case of an affirmative outcome of step 121, in a step 122 a flagis set to TRUE, an edge of the array 17 is preselected and the followingcycle of operations begins. In a step 123, the driver takes care ofswitching off a number p of light sources 18 starting from thepreselected edge of the array 17. In a step 124, it is checked whetherthe entire region 16 framed by the sensor 4 is still illuminated. In thenegative case, in a step 125 the flag is set to FALSE, and in a step 126the number p is decreased by a number a. Then execution of step 123 andthe subsequent check step 124 are returned to. In the case of anaffirmative outcome of step 124, in a step 127 it is checked whether theflag is still TRUE. In the affirmative case, in a step 128 the number pis increased by a number b, and execution of step 123 is returned to. Inthe case of a negative outcome of step 127, i.e. when the flag has beenset to FALSE in step 125, in a step 129 the numbers a, b are decreasedand the flag is set to TRUE. In a step 130 it is checked whether thenumbers a, b are at value 0. In the negative case, step 128 is returnedto. In the affirmative case, the current value of p indicates the lightsources 18 to be switched off starting from the preselected edge of thearray 17, and thus a temporary version of the subset 18 a of the sources18 to be illuminated is set in a step 131. In a step 132 it is thenchecked whether all of the edges of the array 17 have been examined and,in the negative case, step 122 is returned to, wherein a different edgeof the array 17 is of course selected. When all of the edges of thearray 17 have been examined, positive outcome of step 132, the finalsubset 18 a of the sources 18 to be illuminated is set in a step 133.

Wishing to refer to the previous description of the analytical method,also with reference to FIG. 19, selecting the edge of the array as thatof the light source 18 with most negative column index m, this being−m_(min), the value of p=p₁ at the positive outcome of step 130indicates that the column index of the first light source 18 to beswitched on is m₁=−m_(min)+p₁; selecting the edge of the array as thatof the light source 18 with maximum column index, this being m_(max),the value of p=p₂ at the positive outcome of step 130 indicates that thecolumn index of the last source to be switched on is m₂=m_(max)−p₂;selecting the edge of the array as that of the light source 18 with mostnegative row index, this being −n_(min), the value of p=p₃ at thepositive outcome of step 130 indicates that the row index of the firstlight source 18 to be switched on is n₃=−n_(min)+p₃; selecting the edgeof the array as that of the light source 18 with maximum row index, thisbeing n_(max), the value of p=p₄ at the positive outcome of step 130indicates that the row index of the last source to be switched on isn₄=n_(max)−p₄. Therefore the light sources of indexes (m₁,n₃), (m₂,n₃),(m₂,n₄), (m₁,n₄) will be switched on.

The cycle of steps 123-130 described above can be carried outsimultaneously for both edges of a one-dimensional array 17 or, in thecase of a two-dimensional array 17, simultaneously for a pair ofopposite edges (i.e. simultaneously determining the row, respectivelycolumn subset) or adjacent edges (i.e. simultaneously determining therow and column indexes of the first source to be switched on startingfrom a vertex of the array); of course, in such a case the variables p,a, b and the flag will be suitably multiplied. In certain configurationsof the image capturing device 2 it may moreover be sufficient to repeatthe cycle of steps 123-130 only on two or three edges of the array 17,for example when the region 16 framed by the sensor 4 on the substrate Sis rectangle-shaped and centred both as seen by the sensor 4, and asseen by the illumination device 6.

It should be understood that the use of numbers a and b allows thenumber of cycles to be overall carried out to be reduced, by carryingout a sort of binary search of the first source of the subset 18 a oflight sources 18 to be switched on starting from the preselected edge ofthe array 17. In other words, as long as the region 16 framed by thesensor 4 on the substrate S is totally illuminated—the flag remainsTRUE—, many (b) light sources 18 are switched off each time in step 128.When too many light sources 18 have been switched off—flag brought toFALSE—, it is attempted to switch off less of them at a time byswitching back on some (a) sources, until meeting the last source thatcan be switched off starting from the edge. In particular in steps 126,129 the decrease and/or increase of a and/or b can occur by successivehalving and/or doubling (dichotomic method) to make the convergence ofthe algorithm faster. However, the use of numbers a and b is optional,it being possible to switch on and off a single source at a time.

Those skilled in the art will understand how to modify the block diagramof FIG. 18 to start from a configuration wherein all of the lightsources 18 are left switched off, and only one or more of them areswitched on at a time, or to start from a configuration wherein thelight sources 18 of a central region of the array 17 are initiallyswitched on.

Moreover, it should be understood that the initial number p of lightsources 18 that are switched off can be selected as a function of thelast determination carried out. Indeed, as the working distance Dincreases (or decreases, respectively), the number of light sources 18to be switched off starting from one edge of the array 17 increases, andthe number of light sources 18 to be switched off starting from theopposite edge of the array 17 decreases (cfr. FIG. 3). Therefore,instead of always starting back from the illumination of the entirearray 17, it is possible to start from the subset 18 a of sourcesdetermined for the closest working distance D.

In the more general case in which the area to be switched on the array17 is a generic quadrilateral and not a rectangle or square, whichgenerally occurs when the planes on which the sensor 4 and the array 17lie are not parallel and in particular in the case of FIG. 17, adifferent embodiment of the empirical/adaptive method is moreadvantageous to implement, both run-time (FIG. 7) and one-off (FIG. 8),the step 101 of determining the subset 18 a of light sources 18 thatmust be switched on, at a given current working distance D within thedepth of field DOF, to illuminate the entire and only the region 16framed by the sensor 4.

This embodiment is based on the following steps, described also withreference to FIG. 20:

a) switching on a series of rows or columns of the array 17 insuccession until the region 16 framed by the sensor 4 is at leastpartially illuminated, in particular until the sensor 4 detects theimage of a line, in general oblique and not centred;b) identifying and switching on a light source 18 of the array 17,indicated as “starting light source” hereinafter, represented by pointG₀ in FIG. 20, which illuminates a point P₀ of such an illuminated line,which in turn illuminates a point F₀ (or photosensitive element 14) ofthe sensor 4; preferably the starting light source is selected as theone that illuminates the middle point of the portion of illuminated lineseen by the sensor 4; the selection can take place for example withrapid sequential switching on of all of the light sources 18 of the rowor column under examination;c) selecting an oriented direction along the array 17, having origin inthe starting light source G₀, and identifying the light source 18(represented by point G₁ in FIG. 20) along such a direction thatilluminates a point P₁ the image of which is formed onto one of thephotosensitive elements 14 at an edge of the sensor 4, represented bypoint F₁ in FIG. 20;d) storing the light source 18 identified, together with thecorresponding edge of the sensor 4;e) repeating steps c) and d) each time selecting an oriented directionangularly spaced from that of the previous execution, until 360° arecompleted, identifying the sources G₂, G₃, G₄ . . . corresponding to thephotosensitive elements F₂, F₃, F₄ . . . ; it should be noted that theedge of the sensor 4 identified each time can be the same as that of theprevious execution, or else the adjacent one; the angular spacingbetween the directions is suitably selected so that there are at leasteight iterations of steps c) and d), preferably at least twelve, so asto identify at least two light sources 18 for each edge of the sensor 4;f) identifying, for each group of sources that illuminate points whoseimage is formed onto one of the photosensitive elements 14 of a sameedge of the sensor 4, like for example the sources G₂, G₃ of FIG. 20,the straight line that joins them on the array 17; andg) connecting such straight lines to form the perimeter of the polygon(quadrilateral) defining the light sources 18 to be switched on.

For a circular/elliptical sensor the method is identical, but obviouslyit does not make sense to distinguish the different edges of the sensor4, and in order to find the boundary of the light sources 18 to beswitched on, starting from the ones identified, a non-linearinterpolation between the positions of the identified sources, known bya skilled in the art, needs to be used.

A possible implementation of such an embodiment is shown in FIG. 21,divided over plural pages.

The aforementioned step a) is thus implemented with a first cycle ofoperations. In a first step 150, a counter QUAD is initialized, forexample at 0. This counter identifies an area of the array 17 in whichthe search of the subset 18 a of light sources 18 of the array 17 to beswitched on is being carried out. In the preferred implementation, thevalue QUAD=0 identifies the entire array 17, while the values QUAD from1 to 4 indicate the four quadrants of the array 17. Other subdivisionsof the array 17 can be used. In the subsequent step 151, the centralcolumn of the area identified by the current value of the counter QUADis switched on, so that when QUAD=0 all of the light sources 18 of thecentral column of the array 17 are switched on. In step 152 it ischecked whether the region 16 framed by the sensor 4 on the substrate Sis at least partially illuminated, or whether at least part of theilluminated line is “seen” by the sensor 4. In the negative case onepasses to a step 153 in which the column of light sources 18 currentlyswitched on is switched off, and the central row of the area identifiedby the current value of the counter QUAD is switched on, so that whenQUAD=0 all of the light sources 18 of the central row of the array 17are switched on. In a subsequent step 154 the checking of whether theregion 16 framed by the sensor 4 on the substrate S is at leastpartially illuminated, or whether at least part of the illuminated lineis “seen” by the sensor 4, is repeated. In the negative case the QUADparameter is increased by 1 in a step 155 and, in a step 156, it ischecked that all of the areas in which the array 17 has been ideallydivided, in particular all four quadrants (QUAD>QUAD_(max), inparticular QUAD>4), have not been used up. In the affirmative case, themethod ends since there is a design error of the reader 1 or amalfunction thereof. If the quadrants have not yet all been explored(QUAD≦QUAD_(max)), the execution of step 151 is returned to, thereforeswitching on the central column of the quadrant being considered (thecentral row of the quadrant being considered in step 153). If step 152or step 154 gives a positive outcome, then this means that the region 16framed by the sensor 4 on the substrate S is at least partiallyilluminated by the line currently switched on on the array 17. It shouldbe noted that if the reader 1 is suitably designed, the subset 18 a oflight sources 18 of the array 17 to be switched on at any readingdistance D within the depth of field DOF is of neglectable size withrespect to the total size of the array 17, and usually the iterationwith QUAD=0 is sufficient.

In a step 158 the aforementioned step b) is implemented, in other wordsa single light source 18 of the array 17, belonging to the line (row orcolumn) currently switched on and selected such as to illuminate a point“seen” also by the sensor 4, is identified and switched on; preferablythe starting light source is selected as the one that illuminates themiddle point of the portion seen by the sensor 4 of the illuminated lineon the substrate S. Step 158 can for example consist of identifying thephotosensitive element 14 of the sensor 4 intermediate between thosecurrently illuminated, and then carrying out a rapid sequentialswitching on of all of the light sources 18 of the row or column underexamination, each time evaluating the output of such a photosensitiveelement 14.

After step 158, a cycle of operations is carried out that implementsteps c), d), e) outlined above. In a step 159 four service variablesfor such a cycle are initialized: DIR=1, SENSOR_EDGE=FALSE and twopositive integer values H, L, the significance of which will becomeclear hereinafter. The first variable indicates along which orienteddirection on the array 17 the search of the light source 18 thatilluminates a point the image of which is formed on one of thephotosensitive elements 14 at one edge of the sensor 4 is being carriedout. The variable DIR can for example go from 1, which is the column orrow, respectively, along which step 152 or step 154, respectively hasbeen successful, to the maximum number of directions along which thesearch is carried out, MAX_DIR. Every direction is rotated on the array17 by an angle, constant or not, with respect to the previous one, andpreferably it is rotated by 45° so as to obtain eight orienteddirections, or by 30° so as to obtain twelve oriented directions. Thesecond variable SENSOR_EDGE is a flag that indicates whether the lightsource 18 searched for (i.e. that illuminates a point whose image isformed onto one of the photosensitive elements 14 at an edge of thesensor 4), along the direction DIR, has been found.

At this point, in a step 160 another H sources of the array 17 areswitched on in the oriented direction DIR. Then follows step 161 inwhich it is checked whether at least one of the photosensitive elements14 of one of the edges of the sensor 4 is illuminated. In the negativecase it is checked in a step 162 whether SENSOR_EDGE=TRUE; in thenegative case, like in the first execution of step 162, step 160 isreturned to, therefore “lengthening” the line switched on in thedirection DIR by H sources.

When in step 161 it is found that at least one of the photosensitiveelements 14 of one of the edges of the sensor 4 is illuminated, outputYES, a step 165 is carried out in which the flag SENSOR_EDGE is broughtto TRUE; in a subsequent step 166 the values H and L are decreased; andin a subsequent step 167 it is checked whether H=0 and L=0.

In the negative case, i.e. if the numbers L, H are still positive, step168 follows in which the light sources 18 switched on in direction DIRare decreased by L, in other words L light sources 18 are switched off,from the extreme of the line along the oriented direction DIR oppositeto the starting source. Then 161 is returned to, therefore evaluatingwhether the photosensitive element 14 of the edge of the sensor 4 isstill illuminated. In the affirmative case steps 165-168 are repeated,therefore each time switching off an increasingly small number L ofsources, i.e. shortening (but each time by less) the illuminated line inthe direction DIR.

When the checking step 161 has a negative outcome, but it had previouslyhad a positive outcome, the check of step 162 is positive sinceSENSOR_EDGE is TRUE; therefore a step 163 in which the values of thevariable H and of the variable L are decreased, and a step 164 in whichthe flag SENSOR_EDGE is brought back to FALSE are carried out;thereafter execution of step 160 is returned to. In these conditions,indeed, the photosensitive element 14 on the edge of the sensor 4 hadbeen illuminated but it no longer is, for which reason one starts overto “lengthen” the illuminated line in the direction DIR, to go back toilluminate towards the edge of the sensor 4, but lengthening by asmaller amount.

The aforementioned steps are repeated until the values H, L are bothzero, positive outcome of step 167, which indicates that the lightsource 18 that illuminates a point whose image is formed on one of thephotosensitive elements 14 at an edge of the sensor 4 has beenidentified. A value indicative of such a light source 18, typically itspair of row and column indexes, is stored in a step 169, together withthe corresponding edge of the sensor 4, therefore implementing theaforementioned step d).

After step 169 a step 170 of checking whether the last search directionhas been reached, namely whether DIR>MAX_DIR, is carried out; in thenegative case in step 171 the flag SENSOR_EDGE is brought back to TRUEand the counter DIR is increased by 1, then in step 172 all of the lightsources 18 currently switched on (along the line with the previous valueof DIR) are switched off apart from the starting source, after whichstep 160 is returned to, repeating the entire cycle of searching thelight source 18 that illuminates up a point whose image is formed on oneof the photosensitive elements 14 on the same edge of the sensor 4 or onthe adjacent one, and storing it together with the corresponding edge ofthe sensor 4.

In the case of a positive outcome of step 170, the repetition of step e)identified above has ended. Then one passes to the implementation ofsteps f) and g), respectively through a step 173 in which the straightlines that join up, on the array 17, the light sources 18 thatilluminate points corresponding to photosensitive elements 14 of a sameedge of the sensor 4, are found, through interpolation, and a step 174in which such straight lines are connected, defining the vertexes of theperimeter of the light sources 18 a to be switched on on the array 17.

The use of parameters L, H is not strictly necessary, but it allows thesearch of the light source 18 that illuminates the point correspondingto a photosensitive element 14 of an edge of the sensor 4 to be sped up.Preferably, the parameters L, H are initially set at a power of 2, andhalved each time. Alternatively, they can be decreased each time by aconstant number, in particular by 1.

Alternatively, the light sources 18 could be switched on one at a timealong each direction DIR, until the one that illuminates the pointcorresponding to a photosensitive element 14 of an edge of the sensor 4is directly identified.

The evaluation of whether and in what way the region 16 framed by thesensor 4 is illuminated, carried out in steps 121, 124, 152, 154 and161, can be carried out through an automatic analysis of the imageoutput by forming device 3 of the image capturing device 2.

This automatic evaluation can be sped up if, instead of basing it on theanalysis of the entire output image, it is based on the analysis ofportions of image, in particular in the case of a one-dimensional sensor4 on the analysis of the edges of the image, and in the case of atwo-dimensional sensor 4 on the analysis of the rows and columns thatconstitute the perimeter of the image, or upon the analysis of only thecentral column and/or row. This type of partial analysis exploits a wellknown possibility of image sensors, called ROI or Multi-ROI, whichallows one or more regions of interest (ROI) to be defined, which isbrought in output from the sensor 4 much more rapidly with respect tothe reading of the entire frame. Alternatively or additionally, it ispossible to evaluate an image captured at a lower resolution, i.e.analysing for example alternate photosensitive elements 14 only, of theentire sensor 4 or of one or more regions of interest.

The evaluation of whether and in what way the region 16 framed by thesensor 4 is illuminated, carried out in steps 121, 124, 152, 154 and161, can also be carried out visually by the operator, should the imageacquired by the sensor 4 be displayed on the output device 10. In thiscase the user will supply adequate feedback to the reading system 1,through the manual input device 11 of control signals and/or data, whichwill be used like the flag of the method of FIG. 18. Otherwise there canbe two or more controls that allow the user to increase or decrease,respectively, the number of sources switched on (or off) starting fromeach edge of the array 17, thus carrying out analogous functions tothose of blocks 126, 128, 129, 163, 166.

It must be noted that, in the case of run-time determining with adaptivemethod and automatic evaluation of the image, a further factor comesinto play, namely the inclination of the substrate S with respect to thereception axis Z. When these are not perpendicular, the distances of thevarious points of the region framed 16 by the sensor 4 are within arange of distances about an average working distance D and, in thiscase, the adaptive method will give as a result the switching on of adifferent subset 18 a of light sources of the array 17 from that in thecase of a substrate S perpendicular to the reception axis Z; however, ifthe image capturing device 2 is correctly designed, there is never anoccasion where all of the light sources 18 of an array 17 sized to havean emission angle T₀ equal to the required minimum emission angle areswitched on at the same time.

An abbreviated form of the adaptive method can also be used to refinethe selection of the subset 18 a of light sources 18 determined withanalytical method (for example the one described above), for example tocorrect imprecisions of the array 17 of light sources of each imagecapturing device 2 of a production batch. In this case, steps 123-131 or160-169 are carried out only in the neighbourhood of the subset 18 acalculated with analytical method, in other words starting from numbersp, H, L indicative of the boundary (indexes m, n) of such a subset 18 a.

FIGS. 22-27 schematically illustrate some particularly advantageousembodiments of a device 2 for capturing images. For the sake ofsimplicity of presentation, all of the embodiments are described in aplane that is assumed to contain the illumination axis A and thereception axis Z, a or the main direction of the sensor 4, and a or themain direction of the array 17, believing that they are sufficientlydescriptive of the more general case, including the case of a curvedarray (FIG. 6), in the light of the previous teachings.

According to the embodiment of FIG. 22, the image forming device 3 isaccording to one of the embodiments of FIGS. 11, 13 with receiver optics5 coaxial with the sensor 4, or one of the embodiments of FIG. 14 or 16.The illumination device 6 is according to one of the embodiments ofFIGS. 11, 13 with illumination optics 19 a, 19 c coaxial with the array17, or one of the embodiments of FIG. 14 or 16. The reception axis Z istherefore perpendicular to the sensor 4 and the illumination axis A istherefore perpendicular to the array 17. The illumination axis A isparallel to, but does not coincide, with the reception axis Z. The array17 and the sensor 4 can therefore be arranged coplanar, andadvantageously on a same support, on a same integrated circuit board, orbe made on a same integrated circuit substrate. It should be noted thatin this case the illumination device 6 should be designed to have anoverall solid emission angle—i.e. corresponding to the maximumillumination beam T₀—greater than the required minimum solid emissionangle, and thus some light sources 18 of the array 17 are alwaysswitched off. In order to reduce such a drawback, the array 17 couldalso be arranged parallel, but not coplanar with the sensor 4. Thisembodiment has the advantage of being simple to design and assemble.

The illumination device 6 according to the embodiments of FIGS. 23-27described hereinafter can, on the other hand, be designed to have asolid emission angle equal to the required minimum solid emission angle,so that no light source 18 of the array 17 is always switched off, andthe array 17 is fully exploited.

According to the embodiment of FIG. 23, the image forming device 3 isaccording to one of the embodiments of FIGS. 11, 13 with receiver optics5 coaxial with the sensor 4, or one of the embodiments of FIG. 14 or 16.The illumination device 6 is according to one of the embodiments ofFIGS. 11, 13 with illumination optics 19 a, 19 c not coaxial with thearray 17, or one of the embodiments of FIG. 15 or 17. The reception axisZ is therefore perpendicular to the sensor 4, while the illuminationaxis A is inclined with respect to the plane of the array 17 by an angleindicated here with θ₀. The illumination axis A is inclined with respectto the reception axis Z by an equal angle θ=θ₀. The array 17 and thesensor 4 can therefore be arranged on parallel planes, in particularcoplanar, with the advantages outlined above with reference to FIG. 22.It should be noted that if for the illumination device 6 theconfiguration of FIG. 17 is used, the illumination planes could, notvery advantageously, be very inclined.

According to the embodiment of FIG. 24, the image forming device 3 isaccording to one of the embodiments of FIGS. 11, 13 with receiver optics5 coaxial with the sensor 4, or one of the embodiments of FIG. 14 or 16.The illumination device 6 is according to one of the embodiments ofFIGS. 11, 13, with illumination optics 19 a, 19 c coaxial with the array17, or one of the embodiments of FIG. 14 or 16. The reception axis Z istherefore perpendicular to the sensor 4, and the illumination axis A istherefore perpendicular to the array 17. The sensor 4 and the array 17are arranged on planes forming an angle θ₁ between them, so that theillumination axis A is inclined with respect to the reception axis Z byan equal angle θ=θ₁.

According to the embodiment of FIG. 25, the image forming device 3 isaccording to one of the embodiments of FIGS. 11, 13 with receiver optics5 coaxial with the sensor 4, or one of the embodiments of FIG. 14 or 16.The illumination device 6 is according to one of the embodiments ofFIGS. 11, 13 with illumination optics 19 a, 19 c not coaxial with thearray 17, or one of the embodiments of FIG. 15 or 17. The reception axisZ is therefore perpendicular to the sensor 4, while the illuminationaxis A is inclined with respect to the plane of the array 17 by an angleindicated here with θ₀. The sensor 4 and the array 17 are arranged onplanes forming an angle θ₁ between them, so that the illumination axis Ais inclined with respect to the reception axis Z by an angle θ=θ₁+θ₀.This embodiment allows small absolute values of the angles θ₁ and θ₀,and therefore a small size of the image capturing device 2, to bemaintained, still obtaining a large angle θ and a greater designflexibility by having two parameters on which to act. This embodiment isparticularly useful when the depth of field DOF is concentrated in anarea close to the reader 1.

According to the embodiment of FIG. 26, the image forming device 3 isaccording to the embodiment of FIG. 17. The illumination device 6 isaccording to one of the embodiments of FIGS. 11, 13 with illuminationoptics 19 a, 19 c coaxial with the array 17, or one of the embodimentsof FIG. 14 or 16. The illumination axis A is therefore perpendicular tothe array 17, while the reception axis Z is inclined with respect to theplane of the sensor 4 by an angle indicated here with θ₂, so that theillumination axis A is inclined with respect to the reception axis Z byan equal angle θ=θ₂. The array 17 and the sensor 4 can therefore bearranged on parallel planes, in particular coplanar, with the advantagesoutlined above with reference to FIG. 22.

According to the embodiment of FIG. 27, the image forming device 3 isaccording to the embodiment of FIG. 17. The illumination device 6 isaccording to one of the embodiments of FIGS. 11, 13 with illuminationoptics 19 a, 19 c not coaxial with the array 17, or one of theembodiments of FIG. 15 or 17. The illumination axis A is thereforeinclined with respect to the plane of the array 17 by an angle indicatedhere with θ₀, and the reception axis Z is inclined with respect to theplane of the sensor 4 by an angle indicated here with θ₂. The array 17and the sensor 4 can therefore be arranged on parallel planes, inparticular coplanar, with the advantages outlined above with referenceto FIG. 22, and the illumination axis A is inclined with respect to thereception axis Z by an angle θ=θ₀+θ₂. This embodiment also allows smallabsolute values of the angles θ₀ and θ₂, and therefore a small size ofthe image capturing device 2, to be maintained, still obtaining a largeangle θ and a greater design flexibility by having two parameter onwhich to act.

The common, non-inverting illumination optics 19 a of the embodiments ofFIGS. 13 and 16 can also be arranged with its axis inclined with respectto the array 17, analogously to what has been described with referenceto FIG. 17. Such an illumination device 6 can advantageously be used inthe embodiments of the image capturing device of FIGS. 23, 25, 27.

Moreover, the provisions of FIGS. 11 and 17 can be combined, byarranging the inverting illumination optics 19 a inclined and offsetwith respect to the array 17, to obtain angles of inclination θ₀ betweenthe illumination axis A and the normal to the plane of the array 17 of alarge value, with a smaller increase in the overall size of the imagecapturing device 2, particularly useful when the depth of field DOF isconcentrated in an area close to the reader.

With reference to FIG. 28, which refers to the illumination device 6 ofthe embodiment of FIG. 11, when the array 17 is positioned in the objectplane of an inverting-type projection lens 19 a, through a suitableselection of the f-number of the projection lens 19 a it is possible tokeep the illumination beam emitted by the array 17 of light sources 18focused for a suitable range of distances in front of the illuminationdevice 6. Such a range of distances should correspond at least to thedepth of field DOF of the sensor 4 of the image capturing device 2.

Such a range of distances, known in literature as image side depth offocus, (W. J. Smith, “Modern Optical engineering,” 3rd ed., ed. McGrawHill 2000, chap. 6.8), is different according to whether measurement istaken, from the distance D′ at which the projection lens 19 a isfocused, going away from the projection lens 19 a (δ′) or going towardsthe projection lens 19 a (δ″). However, for large values of the distanceD′, this difference can be neglected assuming δ′=δ″, and the range ofdistances is approximately equal to δ′=D′²*κ/W_(a)=D′K′/W_(a), where K′is the maximum design magnification for the image 22 _(m) of each lightsource 18 on the substrate S, in mm, K is the same amount expressed inangular blur (K′=D′*tgK), and W_(a) is the aperture of the projectionlens 19 a. For small angles, like in the cases examined here, κ≈ω_(m) orκ≈ω′_(m), where the angles ω_(m) ω′_(m) are indicated in FIGS. 14-16.

The higher the working f/number (D′/W_(a)) of the projection optics 19 aand the focal distance (D′), the greater the image side depth of focus6″, 6′. Assuming for example to focus the illumination beam T, having anemission angle of ±25°, at a distance D′=350 mm from the projection lens19 a, and accepting an angular blur K equal to about 2.5% of the size ofthe illuminated area, i.e. κ=1.25°, a working f-number of 35 issufficient to have an image side depth of focus δ′≈δ″=267 mm, i.e. tokeep the image projected by the array 17 on the substrate S focused forthe entire depth of field DOF of the image forming device 3, if DOF=2δ′.

By selecting the aperture W_(a) of the projection lens 19 a between 5and 20 mm, preferably between 6 and 12 mm, and the focal distance D′ ofthe illumination device 6 between 100 and 350 mm, it is possible toobtain an image side depth of focus δ′ having typical values for theapplication, in other words typical values of the depth of field DOF andof the minimum reading distance D₁ and of the maximum reading distanceD₂ of the image forming device 2.

Thus, provided that the projections optics 19 a is suitably selected, itis possible to obtain an image projected by the illumination device 6,which is the projection of the array 17 of light sources 18, havingclean edges at every working distance D.

Similar considerations apply to the illumination devices of theembodiments of FIGS. 13-17.

In the embodiments of the illumination device 6 of FIGS. 11, 13, 16, 17,the illumination optics 19 a or 19 c preferably comprises a collimationlens, having for example a constant angular magnification law AMAG_(a),preferably with angular magnification ratio 0.7. The illumination optics19 a, 19 c preferably has a fixed focal length.

As a specific example, let us consider the configuration of FIG. 24,with the illumination device of FIG. 11, with a one-dimensional array 17lying in the plane Z, Y (plane of FIG. 24) and having a pluralitym_(tot)=52 of light sources 18 arranged along axis Y and spaced apartfrom one another by M=100 μm, for an overall length of 52*100 μm=5.2 mm.Let us assume that the angle of inclination θ₁ between the illuminationaxis A and the reception axis Z is θ₁=14°, so that cos α₁=1.000, cosα₂=0.000, cos α₃=0.000, cos α₄=0.000, cos α₅=0.970, cos α₆=−0.242, cosα₇=0.000, cos α₈=0.242, cos α₉=0.970. The illumination vertex A₀ is at adistance y₀ from the reception vertex O within the range between 0 and20 mm, for example y₀=−10 mm, and is displaced forward along the axis Zby 10 mm, and therefore has coordinates A₀(0,−10,10). Let us also assumethat the image capturing device 3, with one-dimensional sensor 4 lyingalong axis X and centred around the origin O, has a constant andsymmetrical field of view around the axis Z, defined between β₁=+20° andβ₃=−20° (typically the field of view β₁=β₃ is between 10° and 30°). Letus also assume that the depth of field DOF of the sensor 4 is comprisedbetween a minimum working distance D₁=30 mm and a maximum workingdistance D₂=500 mm, such that the depth of field is DOF=470 mm. Let usthen assume that the illumination optics 19 a has a constant angularmagnification law, with magnification ratio AMAG_(a)=0.7, and that thearray 17 is arranged at a distance t=−6 mm from the illumination optics19 a. Applying the formulae (1) to (15), at every distance D the minimumindex m₁ and the maximum index m₂ of the extreme light sources 18 to beswitched on the array 17 to exactly cover the line framed by the sensor4 at that distance are obtained. The progression of such indexes isshown in Table I below, for working distances D sampled with steps of 30mm, 20 mm for the last step.

TABLE I D m₁ m₂ 30 −25 12 60 −14 21 90 −10 23 120 −9 24 150 −8 24 180 −725 210 −7 25 240 −7 25 270 −6 25 300 −6 25 330 −6 26 360 −6 26 390 −6 26420 −6 26 450 −6 26 480 −5 26 500 −5 26

FIG. 29 provides a visual representation of the subset 18 a of lightsources 18 to be switched on in the array 17, indicated as a continuousstrip that goes from the minimum index to the maximum one.

From the qualitative point of view, from the examination of Table I andof FIG. 29 it is manifest that, the field of view β₁, β₃ or angulartarget being equal, at working distances D close to the maximum distanceD₂ there are no appreciably large changes in the position of the firstand last light source 18 a to be switched on in the array 17, in otherwords the extreme indexes m₁ and m₂ change slowly, while from close by,at working distances close to the minimum distance D₁, the position ofthe first and last light source 18 a to be switched on in the array 17undergoes a greater variation, in other words the indexes m₁ and m₂change faster.

It should be noted that at no working distance D are all of the lightsources 18 of the array 17 switched on, rather at every working distanceD a certain number of light sources 18 starting from at least one edgeof the array 17 are switched off. Moreover, the first and last lightsource 18 are, switched on at the minimum and maximum working distanceD₁, D₂, respectively. As described above, this optimal condition can beobtained with any of the embodiments of FIGS. 23-27 if the solidemission angle of the illumination device 6 (subtended by the maximumillumination beam T₀) is equal to the required minimum solid emissionangle. It is however possible to use the configuration of FIG. 22,simply in this case some light sources 18 of the array 17 will always beswitched off at all working distances D.

From FIG. 29 and/or from a representation thereof in the form of alook-up table, similar to Table I but generally extending to the case ofa two-dimensional array 17, and/or applying the methods described above,the indexes m_(i),n_(i) of the extreme light sources 18 to be switchedon in the array 17 are therefore obtained, thus implementing the step101 of determining the subset 18 a of light sources 18 of the array 17to be switched on at each working distance D within the depth of fieldDOF of the sensor 4 to illuminate the entire region 16 framed by thesensor 4 on the substrate S.

If the determining of the subset 18 a of light sources 18 of the array17 to be switched on to illuminate the entire region 16 framed by thesensor 4 takes place with analytical method, both run-time (FIG. 7) andone-off (FIG. 8), the driver 13 must know the reading distance D.

Such information can be provided by a suitable measurer of the readingdistance, which can be part of the reading system 1 shown in FIG. 2 orbe in communication therewith through the communication interface 9.Such a measurer of the reading distance D can be made in different persé well known ways, for example through a device based on a system ofphotocells, a device based on the measurement of the phase or of thetime of flight of a laser or LED, visible or IR, beam or of the radar orultrasound type, etc.

The intrinsic flexibility of the array 17 of individually drivable lightsources 18 of the illumination device 6 offers however the possibilityof illuminating, on the substrate S, a luminous figure of variableshape, size and/or position in the region 16 framed by the sensor 4 as afunction of the reading distance D, as well as possibly at variablewavelength(s), which allows the reading distance D to be measured orestimated, as well as the presence of a substrate S to be detected, andpossibly the focal condition of the image forming device 3 to bemeasured or estimated.

By acquiring, through the image capturing device 3, an image of thesubstrate S (partially) illuminated by the luminous figure, it istherefore possible to evaluate or even precisely measure the distance atwhich the substrate S is placed, namely the reading distance D.Alternatively, the estimate or measurement of the reading distance D iscarried out by the user, and suitably provided to the driver 13 throughthe manual control and/or data input device 11.

For example, with reference to FIGS. 30 and 31, wherein the imagecapturing device 2 is, by way of an example, according to the embodimentof FIG. 23, the driver 13 can drive the array 17 to switch on a subset18 b of light sources 18 such as to intentionally illuminate only aportion of the region 16 framed by the sensor 4, for example the set ofsources 18 b that emits within a certain predetermined emission anglecp. As the reading distance D changes, due to the parallax error (whichin this case is not corrected, rather intentionally exploited for thispurpose) between the illumination device 6 and the image forming device3, the size and the position of the boundary of the luminous FIG. 23illuminated on the substrate S change within the image captured by thesensor 4. In the depicted case, the luminous FIG. 23 projected is arectangle that starts from an edge of the region 16 framed by the sensor4 and increasingly widens towards its opposite edge as the readingdistance D increases. Analogously, a strip can be projected thatmoves—possibly widening—or a cross in the case of a two-dimensionalarray 17. If the substrate S is absent or outside the depth of fieldDOF, the luminous FIG. 23 does not fall or only partially falls withinthe region 16 framed by the sensor S, or it has an excessive blur, sothat a function of detecting the presence of the substrate S is alsoobtained.

In an alternative embodiment, the driver 13 can drive the array 17 toswitch on a configuration 18 b of light sources 18 such as to project apair of inclined bars, which, by changing position on the substrate Saccording to the reading distance D, form a luminous figure thatcontinuously changes among two separate bars, a V, an X, an inverted Vand two separate bars with opposite inclination to the initial one, asdescribed for example in the aforementioned EP1466292B1. The X shape canadvantageously be associated with the optimal focal distance of theimage forming device 3. In another embodiment, the driver 13 can drivethe array 17 to switch on a configuration 18 b of light sources 18 suchas to project a pair of crosses, which, by changing position on thesubstrate S according to the reading distance D, form a luminous figurethat continuously changes among two distinct crosses, and possiblydifferently inclined to each other, and a single cross at the workingdistance D at which they overlap, which can advantageously be associatedwith the optimal focal distance of the image forming device 3, asdescribed for example in the aforementioned U.S. Pat. No. 5,949,057. Theestimate or measurement of the working distance D can also exploit thefact that the luminous FIG. 23 projected onto the substrate Sprogressively loses definition, in other words it blurs, moving awayfrom the optimal focal distance of the image forming device 3, asdiscussed above with reference to FIG. 28. These embodiments, and otheranalogous ones, therefore also allow a function of estimating orevaluating the focal condition, and/or of its visual information to theuser, in the case of illumination in the visible range, to beimplemented with the image capturing device 2. In the case for exampleof projection of two oblique bars, the luminous figure is alsoadvantageously indicative to the user of the direction in which tomutually displace the image capturing device 2 and the substrate S inorder to achieve the focused condition.

Alternatively or additionally, after the measurement or automaticestimate of the working distance D, or based on the information receivedfrom a device external to the image capturing device 2, the driver 13can drive the array 17 to switch on a configuration 18 c of lightsources 18 such as to project onto the substrate S, at the distance D, aluminous FIG. 24 in the visible spectrum, and that is straightforward tounderstand, for example the words “TOO FAR”, “TOO CLOSE”, possiblyaccompanied by a blurred condition thereof, made through a suitablematching of the focal distances of the array 17 and of the receptiondevice 3, so as to further convey the intended meaning, and possibly theword “OK” in focused condition, as schematically illustrated in FIGS.32-34.

It should be noted that while the configurations 18 b described aboveare switched on by the driver 13 before having determined the subset 18a of light sources 18 that illuminate the entire region 16 framed by thesensor 4 on the substrate S, the configuration 18 c now described can beswitched on by the driver 13 after having determined the subset 18 a oflight sources 18 that illuminate the entire region 16 framed by thesensor 4 on the substrate S, and therefore it can advantageously becentred with respect to such a subset 18 a, as shown in FIG. 34.

The intrinsic flexibility of the array 17 of individually drivable lightsources 18 of the illumination device 6 also offers the possibility ofimplementing an outcome indication device. In such an operating mode,the driver 13 drives the array 17 to switch on a configuration of lightsources 18 such as to illuminate, on the substrate S, a luminous FIG. 25indicative of the positive or negative outcome, and possibly of thereasons for a negative outcome, of an attempt at capturing an imageand/or decoding the optical information C, for example an “OK” asalready shown by the configuration 18 c of light sources 18 in FIG. 34,or a “NO” made in an analogous way. As an alternative or in addition tosuch changes in shape of the luminous FIG. 25 for indicating outcome,changes in size, colour and/or position of the luminous figure can beused, for example any green coloured luminous figure will indicate apositive outcome, while a red coloured luminous figure will indicate anegative outcome. Also in this case the configuration 18 c is preferablycentred with respect to the subset 18 a.

The intrinsic flexibility of the array 17 of individually drivable lightsources 18 of the illumination device 6 also offers the possibility ofimplementing an aiming device.

Thus, for example, in order to supply an image for aiming at the entireregion 16 framed by the sensor 4, which aids the operator to positionthe reader with respect to the optical information C by displaying onthe substrate S a visual indication of the region 16 framed by thesensor 4, the driver 13, once the subset 18 a of light sources to beswitched on to illuminate the entire region 16 framed by the sensor 4has been defined, can drive the array 17 to switch on one or a certainnumber of light sources 18 d at the edges of such a subset 18 a or nearto them, so as to illuminate the boundary of the region 16 framed by thesensor 4, or one or more sections thereof, like for example the cornersin the case of a two-dimensional sensor 4, as schematically shown by theluminous aiming FIG. 26 in FIG. 35. Alternatively or additionally, thedriver 13 will take care of illuminating one or a certain number oflight sources 18 at intermediate sections of the four sides of therectangle or quadrilateral defined by the subset 18 a, and/or a certainnumber of light sources arranged as a cross at the centre of therectangle or quadrilateral defined by the subset 18 a.

There are also various applications in which it may be advantageous forthe image capturing device 2 to only capture one or more regions ofinterest ROI within the region 16 framed by the sensor 4. The provisionof the plurality of individually drivable light sources 18 of the array17 allows a corresponding partial illumination and/or the aiming of suchregions of interest ROI to be easily obtained. In this case the driver13 drives the array 17 of the illumination device 6 to switch on onlyone or more configurations 18 e (not shown) of sources 18 of the subset18 a, determined according to one of the methods outlined above, eachsized and positioned with respect to the subset 18 a in a waycorresponding to how the associated region of interest ROI is sized andpositioned with respect to the entire region 16 framed by the sensor 4on the substrate S.

A first application consists of configuring a reader 1 having atwo-dimensional sensor 4 as a linear reader. In order to increase theframe rate and the reading promptness, it is possible and per se knownto reduce the number of active lines of the sensor 4 to a few only (downto one); in this situation the region of interest ROI is a thinrectangular area, down to a line, ideally arranged at the centre of thevertical field of view β₂, β₄ or horizontal field of view β₁, β₃,respectively. The configuration 18 e of light sources 18 switched on bythe driver 13 thus comprises the or some intermediate sources of thesubset 18 a in one direction and all of the sources of the subset 18 ain the perpendicular direction, so as to project onto the substrate S athin strip of light at the region of interest ROI.

A second application is the processing of the image of documents instandardised format, or forms. As an example, FIG. 36 illustrates adocument or form 200 comprising different types of information to beprocessed, in particular:

-   -   an area 201 comprising encoded information in OCR (optical        character recognition) format, in other words writing done in        characters able to be recognised by a suitable software;    -   an area 202 comprising one or more optical, linear and/or        two-dimensional codes;    -   an area 203 comprising other encoded information in graphical        form, such as hand-written text, signatures, trademarks or        logos, stamps or images.

Through suitable processing of a first image captured by the sensor 4,or of a part thereof, possibly in low resolution, it is possible, in aper se well known way, to locate the position of such areas 201-203within the region 16 framed by the sensor 4, which for the sake ofsimplicity of presentation is assumed to coincide with the entiredocument 200. In the case in which the region 16 framed by the sensor 4extends beyond the entire document 200, this can be considered a furtherregion of interest.

Once one or more of such areas 200-203 has/have been located, the driver13 can drive the array 17 to switch on only the light sources 18 thatilluminate, in a manner analogous to what has been described withreference to FIG. 35, the centres and/or the boundary, at least in part,of the located area(s) 200-203, to act as an aid for aiming and/or forthe interactive selection of the located areas to be actually processed,as shown by the aiming luminous figures 26,26 ₁,26 ₂,26 ₃, in FIG. 36.

The interactive selection by the user can take place for example throughpresentation of the different areas 201-203, and possibly of the entireregion 16 framed by the sensor 4, with different numbers associated,also projected by the illumination device 6 itself, near to or at theaiming luminous figures 26,26 ₁,26 ₂,26 ₃, of the located areas 200-203,or through presentation of the different aiming luminous figures 26,26₁,26 ₂,26 ₃, with different colours, in the case in which the lightsources 18 are suitable for emitting, individually or as a whole,according to at least two different wavelengths in the visible field.Each number or colour can for example have a different button of themanual input device 11 of the reader 1 associated with it, or there canbe one or two buttons for cyclically selecting among the different areas200-203, the selection becoming final after a certain time, or bypressing a further button, or in another suitable way. The area 200-203selected on each occasion can be highlighted for example through greaterillumination, intermittent illumination or similar, or every time theselection button is pressed a single area 201-203 can be illuminated ata time.

For the same purpose of interactive selection, or in a subsequent stepto the selection by the user of one or more of the located areas200-203, the driver 13 can drive the array 17 to switch on aconfiguration 18 e comprising only the light sources 18 that illuminatethe located area(s) 200-203, to provide an optimised illumination forthe purposes of capturing the image of such areas, as shown for exampleby the luminous regions 27 ₂,27 ₃ in FIG. 37.

In the case of a reader 1 used with standardised documents or forms, thesize and positions of the aiming figures 26, 26 _(i) and/or partialillumination figures. 27, 27 _(i) within a region 16 framed by thesensor 4 corresponding to the entire form 200 can be preset in thereader 1 in a configuration step instead of being located run-time.

As a further application, in the case of an unattended reader 1, forexample for reading optical codes C carried by objects in relativemovement with respect to the reader 1, for example on a conveyor belt,the driver 13 can drive the array 17 to switch on a configuration 18 fcomprising only the light sources 18 that illuminate the area where theoptical code C has been located.

Also for the aiming and/or the selection of regions of interest and/orof the entire region 16 framed on the substrate S, instead of theillumination of their centres and/or boundaries, at least in part, thesecan be totally illuminated (FIG. 37).

In a further embodiment, shown in FIG. 38, two arrays 17, 17 a ofindividually drivable light sources 18 can be arranged on opposite sidesof the sensor 4 of the image forming device 3. The two arrays 17, 17 acan be driven by the driver 13 so as to each illuminate at most onerespective half 28, 28 a of the region 16 framed by the sensor 4. Inthis case it is possible to more easily illuminate a large region 16framed by the sensor 4.

Alternatively, the two arrays 17, 17 a can be driven by the driver 13 ina symmetrical manner, with respect to the reception axis Z, so as todouble the radiant flux density in the entire region 16 framed by thesensor 4, or in one or more region of interest thereof, by overlappingthe emissions of the two arrays 17, 17 a, as shown in FIG. 39. A moreuniform illumination of the region 16 framed by the sensor 4 on thesubstrate S is also automatically obtained, since the light sources 18of the array 17 that illuminate less because they are farther from thesubstrate S correspond to light sources 18 of the array 17 a thatilluminate more because they are closer to the substrate S, andvice-versa.

In FIGS. 38 and 39 it is assumed that a non-inverting illuminationoptics is used at both arrays 17, 17 a, for example comprisingindividual lenses 19 b, and non-inverting illumination optics is used atthe sensor 4, but it should be understood that all of the configurationsdescribed above can be used.

Similarly, in a further embodiment (not shown) four arrays 17 ofindividually drivable light sources 18 can be provided, arranged at thefour sides of a rectangular sensor 4, or in particular a square one, ofthe image forming device 3.

In the various auxiliary functions described above, the illuminationdevice 6 can be caused to work at a low “resolution”, in other words inthe subsets 18 a, 18 b, 18 c, 18 d, 18 e, 18 f respectively, onlyalternate light sources 18 can be switched on, or alternate groups ofone or more light sources 18 can be switched on and off, so as toconsume less energy. Alternatively or additionally, the image formingdevice 3 can operate at a low resolution, by analysing only some of thephotosensitive elements 14, for example only alternate photosensitiveelements 14 or groups of photosensitive elements 14, of the entiresensor 4 or of one or more regions of interest, in other words thereader 1 can implement a suitable algorithm for evaluating at least onefirst sample image with low resolution.

Those skilled in the art will easily understand how to apply theconcepts and methods outlined above, in particular the correlation,expressed by the formulae discussed above, between any point P in theworking space region 15 of the sensor 4, and the light source(s) 18 ofeach array 17, 17 a to be switched on to illuminate such a point, inorder to precisely define the criteria that the driver 13 follows forthe selection of which light sources 18 of the array 17, 17 a to switchon, and optionally with what intensity and/or wavelength(s) of emission,to implement the various embodiments and/or the various additionalfunctions to that of illuminating the region 16 framed by the sensor 4,described above with reference to FIGS. 30-37.

Those skilled in the art will understand that, in the variousembodiments described, the number of light sources 18 of the array 17,17 a and/or their density can be selected considering different factors,including: the depth of field DOF of the image forming device 3, thesize and resolution of the sensor 4, the cost, the calculation capacityof the driver 13 or of the processer that builds the look-up table.

It has been found that a suitable number of light sources 18, in thetwo-dimensional case, is at least 32×32, preferably 64×64 or more, or,in the case of a sensor 4 having shape factor 4:3, 44×32, preferably,86×64 or more. Similarly, in the one-dimensional case, a suitable numberof individually addressable light sources 18 is 32 or 64 or more.

The image capturing device 2 described above, and in particular itsillumination device 6, therefore has substantial advantages.

A first advantage consists of avoiding any parallax and perspectivedistortion error between the field of view of the image capturing device3 and the illumination field of the illumination device 6, although theyare not coaxial. This allows energy to be saved since it is notnecessary for the illuminated region to extend beyond the region 16framed by the sensor 4 to take the parallax error into account.

The intrinsic flexibility of the array 17 of individually drivable lightsources 18 also offers the possibility of very easily changing theregion illuminated on the substrate S, without any moving part (apartfrom the embodiment with micromirrors), rather by simply switching on—asdescribed above—all and only the light sources 18 necessary for theillumination of the entire region 16 framed by the sensor 4 on thesubstrate S, in other words those of the subset 18 a, or by switching ononly a part of such light sources 18 of the subset 18 a for the variouspurposes described above. In other words, the provision of the array 17of individually drivable light sources 18 allows the illumination device6 of the invention to be used to carry out one or more other differentfunctions, which according to the prior art are typically implemented bydistinct devices, therefore reducing the costs and the bulk of thereader 1.

The incorporation of one or more of the aforementioned auxiliaryfunctions into a single image capturing device 2 for is innovative andrepresents in itself an inventive aspect, even in the case in which theillumination axis A and the reception axis Z coincide.

A variant to making an array 17 of light sources 18 on a substrateconsists of an array 17 of light sources 18 having an aperture at itscentre such as to allow its concentric arrangement with the imageforming device 3. This solution, which falls outside the scope of claim1, has the advantage of implementing a symmetrical arrangement withrespect to the optical reception axis Z, at the expense of making aperforated support, which is not standard and complicates the design ofthe driver 13.

Similarly to the use of a zoom and/or autofocus system, the maximumillumination beam T₀ of the illumination device 6 can also be madedynamically variable in size and/or in proportions through well knownzoom and/or autofocus systems, such as electromechanical, piezoelectricor electro-optical actuators for moving one or more lenses of theillumination optics, and/or for changing the curvature of one or morelenses of the illumination optics, for example through the use of liquidlenses or deformable lenses, and/or for moving the array 17.

A further solution, which falls outside the scope of claim 1, consistsof making an illumination device through a plurality of relatively fewsegments of OLEDs, in particular through irregular segments of such ashape as to be able to be put together to form a certain number ofpartially overlapping quadrangular figures, for example three. Based onthe reading distance, the irregular segments that make up the figurethat has the least parallax error with respect to the image capturingdevice 3 are switched on. There can also be one or more series ofrectangular and/or angular segments arranged to form one or moreconcentric rectangles around the irregular segments, that can beilluminated to provide an aiming figure.

The illumination optics 19 a, 19 b, 19 c could be absent in the case oflight sources 18 that are sufficiently collimated and emit according tosuitable directions, for example in the case of an array 17 arrangedalong a curved surface (FIG. 6).

In the case of an array 17 arranged along a curved surface (FIG. 6), allof the references to the plane of the array 17 apply to the planelocally tangent to the array 17.

1. An imager type image capturing device, comprising: an image formingdevice including a sensor including a one-dimensional or two-dimensionalarray of photosensitive elements, and defining an optical receptionaxis, at least one reading distance, and a region framed by the sensoron a substrate at said at least one reading distance, an illuminationdevice including an array of adjacent light sources, defining an opticalillumination axis, wherein: the light sources are individually drivableand each light source is adapted to illuminate an area of a size muchsmaller than the size of said region framed by the sensor, the opticalillumination axis does not coincide with the optical reception axis, anda driver of the light sources is adapted to drive the light sources soas to switch off at least the light sources that illuminate outside ofthe boundary of the region framed by the sensor on the substrate at saidat least one reading distance.
 2. The device according to claim 1,wherein each individually drivable light source comprises a singleilluminating element.
 3. The device according to claim 1, wherein saidat least one reading distance at which the driver is adapted to drivethe light sources so as to switch off at least the light sources thatilluminate outside of the boundary of the region framed by the sensor onthe substrate comprises a plurality of reading distances within a depthof field (DOF).
 4. The device according to claim 3, wherein the readingdistances at which the driver is adapted to drive the light sources soas to switch off at least the light sources that illuminate outside ofthe boundary of the region framed by the sensor on the substrate arediscrete from one another.
 5. The device according to claim 3, whereinthe reading distances at which the driver is adapted to drive the lightsources so as to switch off at least the light sources that illuminateoutside of the boundary of the region framed by the sensor on thesubstrate are variable with continuity within the depth of field.
 6. Thedevice according to claim 1, wherein the image forming device furthercomprises at least one receiver optics.
 7. The device according to claim6, wherein the receiver optics comprises at least one single lens oroptical group shared by the photosensitive elements of the sensor and/oran array of lenses, prismatic surfaces and/or diaphragms each associatedwith a photosensitive element or sub-group of photosensitive elements.8. The device according to claim 1, wherein the reception axis coincideswith the normal to the plane of the sensor.
 9. The device according toclaim 1, wherein the reception axis is inclined with respect to thenormal to the plane of the sensor by an angle.
 10. The device accordingto claim 1, wherein the array of light sources is associated with atleast one projection lens.
 11. The device according to claim 10, whereinat least one projection lens is provided, shared by the light sources ofthe array.
 12. The device according to claim 10, wherein each lightsource is provided with an optical element selected from the groupconsisting of its own projection lens, a diaphragm, a prismatic surface,a light guide, a gradient index lens, and combinations thereof.
 13. Thedevice according to claim 1, wherein the illumination axis coincideswith the normal to the plane of the array.
 14. The device according toclaim 1, wherein the illumination axis is inclined with respect to thenormal to the plane of the array by an angle.
 15. The device accordingto claim 1, wherein the illumination axis is parallel to and spaced fromthe reception axis.
 16. The device according to claim 1, wherein theillumination axis is inclined with respect to the reception axis. 17.The device according to claim 1, wherein the array and the sensor arecoplanar.
 18. The device according to claim 1, wherein the array and thesensor are arranged on planes inclined to each another.
 19. The deviceaccording to claim 1, wherein the number of light sources is selected sothat the area overall illuminated on the substrate by the illuminationdevice undergoes a percentage change that is sufficiently small when asingle light source is switched on/off.
 20. The device according toclaim 19, wherein the percentage change is less than or equal to 15%.21. The device according to claim 1, wherein the driver is adapted so asnot to switch on all of the light sources of the array at any readingdistance.
 22. The device according to claim 1, wherein the driver isadapted to switch off all of the light sources that illuminate outsideof the boundary of the region framed by the sensor at the readingdistance, and to switch on all of the sources that illuminate within theboundary of the region framed by the sensor in an operating mode. 23.The device according to claim 1, wherein the driver is adapted to switchon only the light sources that illuminate at least one region ofinterest within the region framed by the sensor in an operating mode.24. The device according to claim 1, wherein the driver responds to ameasurer of, or device for estimating, the reading distance.
 25. Thedevice according to claim 1, wherein the driver is adapted to switch onlight sources of the array selected to project a luminous figure forevaluation of the reading distance in an operating mode.
 26. The deviceaccording to claim 1, wherein the driver is adapted to switch on lightsources of the array selected to overall illuminate a luminous figurefor aiming the region framed by the sensor and/or at least one region ofinterest thereof in an operating mode.
 27. The device according to claim1, wherein the driver is adapted to switch on light sources of the arrayselected to overall illuminate a luminous figure for indicating theoutcome of an attempt at capturing an image within the region framed bythe sensor in an operating mode.
 28. The device according to claim 1,wherein the light sources of the array are individually drivable also inintensity of emission.
 29. The device according to claim 1, wherein thearray of light sources is suitable for emitting light of more than onewavelength.
 30. The device according to claim 1, wherein the array oflight sources is selected from the group consisting of a one-dimensionalarray and a two-dimensional array.
 31. The device according to claim 1,wherein the array of light sources is selected from the group consistingof a flat array and a curved array.
 32. The device according to claim30, wherein the number of light sources of the array is greater than orequal to 32 in the one-dimensional case, or 32×32 in the two-dimensionalcase, respectively.
 33. The device according to claim 1, wherein thedriver is adapted to switch off at least all of the sources thatilluminate outside of the boundary of a first half of the region framedby the sensor at the reading distance, the image capturing devicefurther comprising a second array of individually drivable, adjacentlight sources, defining a second illumination axis, the secondillumination axis not coinciding with the reception axis, and the driverof the light sources being adapted to drive the light sources of thesecond array so as to switch off at least the light sources thatilluminate outside of the boundary of a second half of the region framedby the sensor, complement to the first half.
 34. The device according toclaim 1, wherein the image capturing device further comprises a secondarray of individually drivable, adjacent light sources, defining asecond illumination axis, the second illumination axis not coincidingwith the reception axis, and the driver of the light sources beingadapted to drive the light sources of the second array so as to switchoff at least the light sources that illuminate outside of the boundaryof the region framed by the sensor.
 35. The device according to claim 1,wherein the driver is adapted to run-time determine which light sourcesof the array to switch on or off, respectively, as a function at leastof the reading distance.
 36. The device according to claim 35, whereinthe run-time determining is carried out at least in part based onanalytics performed by the driver.
 37. The device according to claim 36,wherein the driver is adapted to: calculate the coordinates of peculiarpoints of the region framed on the substrate by the sensor in a firstreference system associated with the reception image forming device;transform the coordinates into a second reference system associated withthe illumination device; and calculate the light sources of the arraythat illuminate corresponding peculiar points in the second referencesystem.
 38. The device according to claim 35, wherein the driver isadapted to carry out the run-time determining in a recursive manner,wherein the driver is adapted to switch on a subset of light sources,evaluate the position and/or the extent of the area illuminated on thesubstrate with respect to the region framed by the sensor, and adapt thesubset of light sources based on such an evaluation.
 39. The deviceaccording to claim 38, wherein the subset of light sources to beswitched on is carried out along a plurality of radially spaceddirections.
 40. The device according to claim 39, wherein the subset oflight sources to be switched on is determined by an interpolation of thepositions of the extreme light sources to be switched on along saidplurality of directions.
 41. The device according to claim 1, whereinthe driver is adapted to determine which light sources to switch on oroff, respectively, as a function of the reading distance by reading themfrom a look-up table.
 42. The device according to claim 41, wherein thedriver is adapted to one-off build said look-up table.
 43. The deviceaccording to claim 41, wherein the driver is adapted to receive saidlook-up table as an input.
 44. The device according to claim 1, whereinthe light sources of the array are selected from the group comprisingsolid state light sources and organic light sources, and preferably theyare selected from the group comprising LEDs, OLEDs, microLEDs andmicrolasers.
 45. An imager type reader of optical information comprisingan illumination device according to claim
 1. 46. A computer programcomprising software code adapted to manage in a parametric manner atleast one quantity of an image capturing device according to claim 1and, for an actual value of said at least one quantity, to determine thelight sources to switch on or off, respectively, as a function of thereading distance, and to output a look-up table of the light sources tobe switched on or off, respectively, as a function of the readingdistance.
 47. An optical reader comprising an array of individuallydrivable, adjacent light sources, and a driver adapted to drive thelight sources of the array in an illumination mode, an aiming mode, anda reading outcome indication mode.
 48. An optical reader according toclaim 47, wherein said driver is also adapted to drive the light sourcesin an optical distance measurement system mode.